Not entirely sure how old you are but by the way you’re writing you seem quite young, don’t worry this is something that is very common that every stutterer encounters. The way I get through presentations is by practicing the speech over and over again and marking out areas where I think I’m going to stutter, then using techniques like taking a deep breath before saying the word or the sound I struggle with; (this is something that King George VI did before addressing the commonwealth and Britain that they’re going into war).