SAT for transfer

I'm going to be a first year at University College London this September, and I really don't like the place, I wanted to transfer to Columbia School of GS and although SAT is optional but I want to take it to boost my chances. I feel really embarrassed that I am going to walk into a test centre full of high-school kids as a 19 year old (almost 20 by then) unc, and seriously, this is a really embarrassing thing for me. What do I do😭😭