I agree with the above, too much talk on what you need to do instead of how to do it, which is why you need to seek out someone to show you proper mechanics (agree with SultanofSwat, they are not good).
It's all about learning to use the entire body and the kinectic chain that begins in your feet and moves throw your arm, which is there for the ride,not to do all of the work.
Your velocity will not improve just by throwing hard at this point. And FWIW, when going through adjustments you are going to lose your command.
Perhaps that is why you didn't take the advice given by that pitching coach.
Again, you won't be able to throw hard unless you make major adjustments.
I hate to see young players get info from people who have no idea what they are talking about, be careful.
Best of luck.