Out of Retirement

hey guys,
I have recently come back from 4 years off baseball. (I am 22).
I am pitching for the first time in a game for the first time in 4 years this weekend.
I have thrown one bullpen session and everything feels good. Hitting my spots perfectly with my fastball.
Now I realise that good pitchers always change the hitters eye level, and unfortunately I do not have much in my repetoire.
I pretty much have a 75mph fastball, a good screwball, decent change, average splitter and average slider.
I used to be the regular starter for under 16’s, 18’s and 20’s for my club as well as bullpen for state team.
Now keeping in mind that I will probably only be pitching 3 or 4 innings (starter) against a mix of young fresh players and seasoned oldies, what sort of strategy should I adopt?
At the moment I can hit almost any spot with my fastball, I have confidence in my screwball and some in my changeup. The rest I havent thrown at all for a very long time.

Thank you for your input.

Work down, miss down. If you are confident with your fastball then stick with it, I firmly believe that if you throw 75 or 105 a well located FB is going to always be your best pitch.

Well got my first start. And I strongly believe it will be my last.
Final line read 1IP 6h 6r 4er 0bb 1k.
I got ahead in the count on every batter, spotted my fastball perfectly with decent velocity. But they just kept smashing out line drives. The first two batters hit grounders to third but the throw to first base wasn’t in time on both occasions. Then they just started hitting line drives.
Wtf went wrong? I pitched so well but they just kept hitting me!