So I'm confused.....you didn't get into the "dream school", but that's where you're wanting to transfer....correct? If you're only considering one school, then showcases aren't really an issue. Contact the coach directly and let him know your situation. If he is interested in seeing you play, find a team to play on this summer....there are teams that HS grads play on before they head to college...look for an 18U team...if you still qualify age-wise. I guess I'd also consider the baseball situation at the school....if you're talking about an SEC or other Power 5 team....your lack of playing experience is probably going to be an issue....even with your size and power....but you won't know unless you ask. Email the coach....also have your HS coach email/call him and explain the situation. Almost all D1's have club ball...and some of those teams are actually awfully good. I'd definitely look into it at the school you're heading to....it will allow you to play against some older kids....some of which were very good HS players...and let you see more pitching than just the one year of HS kids you saw
What position are you? Keep in mind that even at mid-majors, almost all of the incoming freshmen were standout players in HS.....and almost all were a SS, CF or C. Those guys can play multiple positions in college, which makes things much easier on a coach. What was your batting average? How many strikeouts? 9 HR's is nice...but not if you hit .210 and struck out 45 times.
Good luck 