Physics is a hard A level - if you want to get an A* in it you'll have to most likely teach yourself the content and spend hours doing practise questions. That being said, if you really like physics and want to leave yourself open to potentially do some form of physics / engineering at uni I'd do it.
Maths is a relatively straight forward pick, it should be easier get an A* in than physics and there are loads of good resources out there to help you.
I can't speak to econ (I don't take it) but from what I've seen of people doing it, it isn't impossible.
If Data Science is your chosen path, check some uni courses just to make sure that they don't require any subject you're not doing. That not making any difference, take the third A level that you think you can most easily get an A* in.