I definitely wouldn't quit over that. You have worked hard to get where you are and deserve to give yourself a desent chance at this career! If I was in this situation, despite my ego, I would enlist the help of someone senior at work that can thouroughly go over the error's with you, perhaps find a trend and then look at techniques to stop this from happening again. You have already taken the right step by admitting you have a problem here - so now take the next steps to right the problem. And remember - errors/mistakes can never be eliminated but can be minimised when you are practising at your best.