1. Your routine is awful and won't do anything for boxing. 2. The reason you're not gaining weight is because you're not eating enough. Simple as that. Your problem is you're trying to gain and lose weight at the same time. It's possible to do this (get rid of fat and build muscle) but it's very difficult. 3. Whatever you do outside of a boxing gym to "prepare" for boxing training for the first time will do very little to help.
12reps should add mass, rather than strength you would get from 1-7 rep range. **** curls. try deadlifts and squats for a whole body workout, these will also help with explosiveness.
If you want to be successful in any sport, you need to forget about aesthetics. Obviously it's a plus, but lifting is about gaining strength and power, not abs. Also, honestly, 30 pound dumbbells won't really do anything, you need to lift heavy weights. But always make sure you lift properly, or you'll get hurt.
