I had, by TSR's standards, poor grades in double science. In the course I did there was more of a focus on chemistry and biology than physics. There are certainly topics in both triple science and A Level Physics that aren't in double science but most of these weren't covered in much depth in triple, so didn't feel like I had an unreasonable disadvantage. I've noticed that most of these appear in A2 Physics, you should already have a decent understanding of physics by then so they shouldn't be hard to understand. I'm not sure how this applies to the other sciences though.