Just refresh yourself on the essentials. You'll probably find that they go over a lot of the basics anyway as the first year is usually a levelling off period to make sure everyone's at the same standard.
I did catch up on some A-level topics during the first year (you will have free time to do this if you need to), so don't think it's the end of the world. Oddly I found degree level maths (mechanical engineering) easier than A-levels despite it being a far higher standard of maths. I guess it just depends.