So I always had a back of the mind sort of fear in magick that it might ruin my life if I do it wrong.
This manifested in my mind a strong illness that whenever I perform a Rite all sorts of negative thoughts comes into my head some times offensive voices. I tried many things to stop it. But nothing seems to work.
Can a negative thought case a Rite to failure or case it to go against me?
More than likely especially if they cause doubt or oppose the intention.
In my experience doubt will be the number one reason why magic doesn’t work. Better to be rightfully fearful than questioning everything. Magic can be unpredictable but it’s not necessarily going to be your fault when it doesn’t work. After all we’re dealing with forces not often seen in daily life.
Always state what you want to happen as specifically as possible if you want more pin-pointed results. That’s why I always add, “do this with no harm to me nor mine”, so you know your good. Otherwise the universe will cut corners to give you want you asked for, but it might not be how you want it.
I don’t know if at a certain point I should “leave” magic, since I happen to think insults, baneful commands and/or similar visualizations (I proceed to correct these 2 things with other thoughts)… without really meaning it.
Sometimes I clarify this to the entities, apologizing and asking that they consider mostly what I say out loud or whisper. I try also to apply the advice (in meditation, for example) to simply ignore disturbing ideas.
This fear can add up to a pretty nasty thoughtform.
Do a banishment, get a good crystal that reduces stress and fear, and do some deep meditations to try to rewire that particular thought process away from causing you fear.
What I learned long time ago is that even the most dangerous rituals will be done with complete success if you focus your attention on the object of your desire.
If you are in the ecstatic mood, mistakes are normal and allowed. It doesn’t mean that you can do improvisations. If you realize during the ritual that you missed something or made some mistake, do it again, start from the beginning. If not, it’s okay. There’s always a good reason for some “mistakes” if your intention comes from your true self.
Keep that in your mind and you won’t have any problems with unwanted worries.
Negative thoughts will always bring only failures.
Good luck!
Umm… If that happens how will I Banish it??? 
I’m not doing it on purpose it’s happening on its own. My mind is not listening to me.
I tried Meditations yogas everything I could find…
Practice vocalising your rituals and spells. So before you do said ritual you have the verbal order of the ritual memorised. You will feel more confident when doing rituals that way.
conjure it then banish it >:)
I’ve had that problem too, one way to take care of it is to state your intention vocally or mentally of what you want and don’t want after the spell is finished, another way is to destroy unwanted manifestations by reading shiva mantra (namah shivaya), by reading that mantra unwanted manifestations are removed cause Shiva rules over the destructive element.
I wonder - when you meditate, are trying to control your mind instead of observing it?
Meditation is about (amongst many, MANY other things) understanding your own mind, the ability to detach from action/reaction thinking dictated by external things, and self-control, what it’s NOT about is sitting effortlessly in perfect lotus position, having a totally clear and one-pointed mindset, and not having any distracting thoughts or sudden bright ideas.
People who thibk they fail to meditate because thoughts come up relentlessly have never been taught this, which is why there is value in having proper teachers and guides IMO.
If you can observe your mind’s internal play and realise that it is fundamentally seperate from the You that observes it, then you will be one step closer to realising these negative ideas are just imaginary things, and that way you will not invest emotion in them.
Emotion is a fuel and also a kind of map for magickal endeavours, removing the emotion from the thoughts is therefore going to de-fang them in terms of their effects on your work.
Other stuff:
Have you tried laughing at it? Imagining it taking an absurd form, like something from a Dr Seuss book perhaps, or some actor or actress who plays a grump (or even some politician you dislike!) and imagine it talking in a silly squeaky voice?
Have you tried thanking it politely and then ignoring it? fear is there to keep us safe and alive, it’s not the enemy, but sometimes (like a smi=oke alatrm in the kitchen) it goes off at the wrong times, trying to rip it out by the roots, shame yourself over it, blame it, etc., this is going to war with oneself and never fruitful.
Check out this page by David Neagle I linked previously in another thread, see what you can adapt to your own needs.