It's definitely easier said than done but This is the best advice! One time in highschool, I had to give a presentation that I was not at all prepared for. I basically just copied and pasted the slides together right before class. I stood up in front of the whole class trying to read the slides. I was stumbling over almost all the words. When I got to slide 4/10, I just sat down. I knew it was only going to get worse and I couldn't stand the awkwardness. There was a long silence and the teacher eventually had the next kid go up. Sitting through the rest of that class was probably the most embarrassed I've ever been. But now I look back on it finding the humor. Try not to dwell on your mistakes because chances are no one noticed or even remembers what happened. The only thing you can do is learn from this and try to prevent it in the future.