Struggling so much with blocks

Struggling so much with blocks I don’t know why my switch flips so fast but recently it has. My blocks are so bad and I can barely even say a sentence smoothly. I have a presentation next week ( a short one where I don’t really have to talk all that much, but I’m still getting stressed about it) and I need to do something, anything, to make it not so bad. I’m tired of making myself look stupid so is there anyone who can give me advice on what to do?