I lied about my GCSEs for uni. What happens?

I’m really desperate to get into this course for computer science, so I just said I had a 7 in maths from November resits but I don’t that’s just what the requirements say. I even doctored the results certificate from my college resits and already sent it to the unis in question. What do I do now? Will they find out? I can code and do all of that stuff anyway, and I only got a 4 because of things that happened in my life preceding my GCSEs in year 11 starting in year 9; such as my aunts death, being shunned by my friends twice, a severe trolling incident on Instagram, being SA’d, amongst other things I can’t say in here. What happens if I just do my computer science degree for the 3 years and never get found out if I just perform well? What happens if I get found out midway through?