"You may be the only one in your league that can throw (assuming that you are throwing it correctly), but you may aslo - depending on your age - be one of the first pitchers in your league to end your career. Why? While the screwball is certainly an effective pitch (who could argue with the success of Carl Hubbell or Fernando Valenzuela, both of whom threw it anywhere from 50 to 100 times a game), you must equally understand that it is one of the most harmful pitches you can throw since it exerts tremendous pressure on the shoulder and elbow joints of the throwing arm. The mechanics of it require you to reverse everything you learned about throwing the curveball (which is in itself a fairly tough pitch to master)."
The role of the screwball in causing injuries is extremely overstated. Thrown properly, it is no more injurious, and generally far less injurious than is a traditional curveball.
The reason is that to throw a screwball, you must pronate your wrist (turn the wrist counter-clockwise). This takes some of the load off of the UCL and for this and other reasons prolongs the life of the elbow. In contrast, a curveball is often thrown by supinating the wrist (turning the wrist clockwise). This is problematic because it focuses the load on the UCL and causes the bones of the elbow to slam together.
The fact that Hubbell, Valenzuela, and others who threw the screwball had arm problems has nothing to do with the screwball. Instead, it's related to how they threw their other pitches.
If you are having problems getting your screwball to bite, it means that you aren't getting enough spin on the ball. That could be related to weakness in your fingers, wrist, and/or forearm. If you are older than 17, then it might make sense for you to do some light weightlifting and/or training with weighted balls.