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MAT prep going terribly. Help!

I've just started MAT prep and I so so so regret not starting sooner. I'm working through past papers and watching solution videos but I just feel so so hopeless. I'm getting about 5/10 in the multi choice but can't figure anything out for the longer questions. I just feel so sick I don't understand why I'm doing so hopelessly. Was trying to stay positive but I'm really struggling.
For context I'm applying for computing at Oxford. I'm a scottish student and got 100% at both National 5 and Higher for Maths and am enjoying Advanced Higher Maths. So why can I not handle any of these? Are they geared towards A-Level Maths & FM students or am I just not as good at maths as I thought? Any advice? I want to get about 70 on the final thing though at this point I'd be happy with a 60-65 and just the hope that my PS is strong enough.