Not sure about the ums gradings and how it works

I am not sure at how UMS works and how it can affect uni applications, I am an international AS Level student. So say, for example, I did Mathematics in January 2023. I got 65/75, 87% on the P1 paper, which is 100/100 (A) UMS according to the Edexcel calculator. And I got 50/75, 67% on the P2 paper, which is 84/100 (A) UMS, and I got 45/75, 60% on the S1 paper, which is 77/100 (B) UMS. That means I get a total UMS score of 261/300, is that 100 UMS since an A is 240/300, or does that only mean that I got an A as my final grade in Math. Do universities look at my UMS score (261/300), or do they only look at the grade I achieved which was an A. And so would full UMS look be 300/300, meaning I would have to score 66/75 on S1, 63/75 on P2, and 55/75 on P1, I feel like this is quite challenging.