When you're up in material In some games, I was up on material, but then lost due to either time pressure or blunders. How should I avoid these type of pitfalls?
I see two things you can consider:


trying to learn how to control your stress.
playing many faster games to get used to play and think more quickly (if you often play games with 15 minutes per side, try to play games with 10 minutes per side).


Therefore you most probably won't often be in this situation anymore.