You don’t need to put down your modules and grades if you don’t want to, just your final grade of a B, so they won’t know by the end of it if you’re retaking or not (plus this doesn’t look that bad as most people end up retaking a module).
And to get an A overall in A Level Maths you need to get 480/600 UMS. You currently have 232, so you only need 248 more. Therefore, if you can average 83 UMS or more between C3 C4 and whatever other module you’re taking you will end up with an A, so its plausible.
Honestly if I were in your position I would just retake C1 being by the time you’re doing C3/4 C1 will seem ridiculously easy, and getting well above 80 UMS or more will be a walk in the park for you, and it won’t look bad on your UCAS application either.
Hoping all goes well!