It might be an idea to contact the college to find out their stance on gap year applications. As long as you're doing something to keep your mathsyness going, you should be fine. Doing lots of mechanics modules is a good idea and a more than adequate alternative to having taken physics.
Make sure you do all the old MAT papers available online, and do them under timed conditions. Remember that MAT is an AS-level paper in terms of the concepts you need to know, so go over the basic trig, log rules, etc. and learn it all really thoroughly.