retaking GCSE maths in gap year

I finished my A levels this year and originally I was planning on going to university to study computer science but I got a 5 in GCSE maths and dont take computer science nor maths for A levels which limited me to some universities and was thinking if I should retake GCSE maths again to improve my grade so that there are more "better" universities I could go to instead of the one im planning on going to in a months time. Universities such as: Lancaster, Cardiff, reading etc
should I take a gap year to resit GCSE maths? I kind of want to but my place at another university was already confirmed and I had already paid money for accommodation. So if I do take a gap year then would I even be able to get a refund for my money and to remove my place from the university? How would I even do it? (if I can)