Am I screwed for getting 25% extra time?

I'm a mature student. Ive not been in education since 2018. Based on UCAT website I need a letter from my psychiatrist saying what access arrangements I need and why.

I have ADHD and autism. I was diagnosed this year. It doesn't mention access arrangements because I wasn't in education when I had my assessments.

I've contacted my RTC provider but they won't do it. My GP won't do it either.

I have nothing but my two reports that don't even say anything apart from generic stuff.

What can I do?