Nice 12-6 curve ball, by the way. Have you tried throwing it harder sometimes and really getting out in front with it? It's good to mix in a low hard curve with that high hook so the hitters can't easily recognize the breaking ball. Understand that I'm not trying to have you stop throwing that curve. It's a nice pitch. There is something to be said for the freeze effect of a good front door breaking ball, but in this age group hitters will begin show the ability to recognize it and to not swing at it until they have two strikes. It's a bad combination when they know it's coming late in the count and can easily recognize it. If you can start off some of the better hitters with hard curves, they will either think fastball and swing over it, or they will recognize it and let it pass and find themselves down 0-1. No good hitter wants to chop a curve into the ground on the first pitch.
A thing I see a lot with people working on tempo--they slow down their movements. Some people equate "slow" with "in control". You can move fast and be in control. It's harder to do, but more conducive to actually throwing harder in the long run.
I have no idea what your tempo looked like in the past, so it's tough to judge your tempo change.
Another thing about tempo is that it can build, as long as it builds at a constant rate. Some people go slow and then get their arm speed up at the end. That's next to impossible to do properly.
I like to have pitchers increase their tempo at hand break and either maintain that speed of movement or accelerate smoothly from there. Think about driving a car, we want the acceleration to be smooth; we don't want to be coasting up the highway on-ramp then have our head slammed against the head rest as we join traffic. Similarly, we don't want to jerk around our throwing arm.
A second observation I have is that you have your glove way outside your frame as your arm comes through. Try to keep that glove out in front and get your body to the glove. It should allow you to delay your shoulder turn and improve hip / shoulder separation for a velocity boost.
Combine this advice from Roger with accelerated hand break (don't break them sooner...when you break them, break them with emphasis). Then keep that glove out there longer and go to it instead of rotating it around your trunk. These things together should give you some better velocity results.
A final thing that I noticed was that you "come off" your fastball from time to time. It's like your hand is coming off the inside of the ball and you are not getting full force behind the ball. It sometimes leaks out high and inside to right handed hitters. Work on consistency of release with fingers behind the ball. I'm not asking you to squeeze the ball any harder--only to get behind your fastball.