Edexcel A Level Maths

So I got my A Level Maths results yesterday, and let’s just say I flopped. :/ I’m looking to retake some units, but I need some advice on which units to retake? My grades are as follows:

C1: 82 (A)
C2: 71 (B)
S1: 65 (C)

C3: 25 (U)
C4: 6 (U)
S2: 2 (U)

I’m taking a gap year right now and money isn’t an issue. I just need advice on which modules to retake so I can be in for a chance of getting an A or B overall.