You could keep Physics and Computing and next year pick up a full Maths A-Level to go alongside those two? Then you would end up with three useful A-Levels: Maths, Physics, Computing.
Or you could check if any colleges near you have a January start for a BTEC Extended Diploma in IT. This will also allow you to go to many universities if you do well in it, but you should check that it is taught well, and which modules you can pick, so that you don't end up disillusioned.
Some of the best universities may not accept a BTEC (especially stand-alone), and some of the better universities will expect you to have taken A-Level Maths alongside, but many average universities will accept it as is, so it depends what you want. Depending also on what kind of profession you aspire to in the future, three A-Levels may be the safer option, if you can do well in them.