A word to the wise.
Never tell your boss that you don't make mistakes. Never. Your boss knows that everybody makes mistakes. If you tell your boss that you don't, your boss will fear that your pride, or lack of self-confidence, or fear of looking stupid, or fundamental dishonesty, will cause you not to confess to errors that you will inevitably make. That cannot be tolerated.
Obviously, you have to try not to make mistakes. You can ask somebody to check behind you. You can leave your glassware out, so you can go back and make sure that you did the dilutions you thought you did. It's fine to tell your boss, if she questions your dilutions, that you wondered about them too and checked your glassware to confirm them. You can offer to re-do your work just to make sure. Check your calculations for the 42,753rd time. Ask someone else to check them. Keep a list, mental or on paper, of things to check for so you don't repeat the same mistake. If you find that you are prone to a particular error, find a way to not make it anymore - that's your responsibility, not your boss's.
And that's really the main thing. Own your work. Look over it before you pass it on, to make sure it's correct and complete. If you don't know how to do something, find out. Own your successes and own your mistakes.