I recently made my first mould and found out it might have been a bad idea to use rattle can spray paint with this being the result



I want to know if I clean away all the paint with standard thinners am I also effecting the gel coat? A quick rub with a cloth soaked in thinners didn't appear to rub of any gel coat so it seems harmless enough but I'd like to know if this is true or that it does effect the coating?

It doesn't look like the paint reacted badly so you may be OK here.
What I would do is this. Keeping in mind you have wax or release between the paint and your mold so the paint should come off fairly easily.
I often use my very thin bladed painters knife (the kind artists use) to scrap the paint off the best you can. Wash it out with water and wet sand the rest of the paint off with 400 or even coarser. If your gelcoat is sound at this point start wet sanding up the grits to 1200 and then compound polish to a high shine. The rest will be standard procedure.
Hope this helps
Fred