Good afternoon!
There are roughly 20 scholarships that I am eligible for and each require an essay but they all have the same prompt. Would it matter if I used the same essay for all 20 scholarships? I mean I don’t think I can write 20 different essays about who I am.
There’s no issue with that. Go ahead!
I would do it. The odds of winning one of those scholarships is incredibly slim unless it’s local. I’m pretty sure that if they decide to publicly recognize your essay, only one organization would do so.
Not being pessimistic, but encouraging 
My daughter tweaked and recycled several of the many essays that she wrote last year for each of the local scholarships that she applied to between March and June. She won almost all of them–mostly because her peers were too tired or lazy to apply for the local scholarships by the end of senior year–but after being called up to the stage numerous times to collect scholarship awards during senior award night I think some of those kids audience were kicking themselves when they starting to add the amounts. Because 500 bucks here, a 1000 there, before long it does add up to quite a bit of extra money.
Good luck!