You need to keep your appt for the MRI and stay completely shut down until you get the results. You seem to be doubting the sports medicine doctor you saw, so maybe convince your parents to get a second opinion from an orthopedic Dr that specializes in "overhead athletes" which will essentially be a dr that fixes baseball players. Maybe one that also does the newer version of Tommy John, they can do if the ligament is not completely ruptured. I believe they use a synthetic tendon and lay it on top of the ligament. (I always get it wrong the difference between ligament and tendon, sorry) I believe it's a 6month vs 12-18month recovery. Or a practice where they have sports medicine and orthopedics combined. This model is one of my favorite, they work together to decide what is best for you be it rest, PRP, surgery, etc.
Hope: My son developed an acute pain in his elbow a few years back. We all panicked thinking he would need TJ surgery. Luckily the MRI showed he had pinched his ulnar nerve (not damaged his UCL) the pain was from the inflamation and was shut down for a brief time (we used it as his 3months down). So there is always hope it's not TJ
Another thing, and I'm not a Dr or a pitching coach, it seemed to me you ramped up really fast from your shutdown period. My son who is a 2022 pitcher takes almost 6 weeks to ramp back up. Were you following a return to throwing protocol? We continue to follow the one our dr gave us after the medical shutdown 4 years ago. If you need it after you have your elbow issue sorted out pm me and I'll dig it out and email it to you.
Best of luck with the MRI. Also, work on your grades! This elbow diversion may change your timelines. You're going to want the best grades possible (sorry, I'm a mom, I have to nag)