joekenn21, I am in a simular position to you. I am a lefty freshmen pitcher, throwing a little slower than you are, around 73-75. I asked a coach that very question. The first thing he said is that he knows kids that are D1 players right now and are dominating and they only throw a four-seam and two-seam fastball. Yet, they can move their pitches with near perfect accuracy and aren't afraid to go inside. I personally have started throwing a change-up in addition to the two types of fastballs, and I have found it very helpful. Although, I always pitch best when I can throw on the inside corners with my fastball, in which case I end up barely using my change-up.