Does your HS team have a radar gun? When you can consistently sit high 80's you need to get that on tape along with the radar gun reading. You need tape from behind home plate which shows the verified velocity on the gun as well as a good view of the movement on each pitch. Get some tape from the side so your arm action can be viewed. Pull together a clip that is less than 60 seconds and send it to the schools you are targeting. Also, make a shorter clip of 10/20 seconds and post to flatground on twitter.
If you can swing the cost of a PBR showcase even better....if you get to high 80's at 6'3" you will be all set.
Weight room is important too, but finding a baseball/pitching workout is critical - try to find a workout that focuses on enhanced mobility, core and lower body strength.