3 vs 4 A Levels

Heyyy I'm in Year 11 and I've started getting my offers, one of which is a great school, but I'm not completely sure about accepting because they make you take 3 A levels (no exceptions) and I'm also doing their "independent programming qualification" since they don't have AS Comp Sci anymore. So, I'd be doing Maths, FM, and Physics. At a couple other schools (less highly regarded though), I'd be able to do Maths, FM, Physics, and Comp Sci.
For context, I'm aiming for Cambridge or Imperial or some similar type of STEM uni, so I'm worried that even though the school has good prep for admissions tests, national competitions etc, that maybe the 3 A Levels might disadvantage me..? I don't mind learning extra qualifications either, since I'd be interested in learning them anyway, but I fear I wouldn't have as competitive/challenging peers and as many opportunities if I went to a school that lets me do 4 A levels.
Any advice is very much appreciated!