Anything is possible....
I'm a former enlisted Marine whose son will be pursuing a Marine Officer commission while going to Norwich University in Vermont.
Lot's of things can happen during your ROTC (any branch - Army, Navy, Air Force or Marine) that could disqualify you from getting a commission. Some of them could be a result of the realizing the military is not for you, could be grades, could be something physical, could do something stupid while at the school - hazing, striking someone, whole host of things - pregnancy! etc...
The "cut" from the program comes from the several areas though while you are attending ROTC classes and while attending OCS in your Junior year. If you are found not to be performing as a qualified leader in ROTC, your cadre of training officers and non-comms are going to be counseling you about a different career track way before you arrive at OCS. They are the ones who are training you before sending you to join their particular branch of service and these people are good at selecting people who should NOT become officers.
Likewise, once you get to OCS the stress level gets bumped up a bit to more of that Drill Instructor stuff we've all seen in movies. While in ROTC the cadre do not engage in that behavior because their role is to assess from a different perspective - can the candidate do the basics? Adhere to a regimented program? Wear their uniform properly? Follow basic instruction and display a military bearing and perform military courtesies?
Your commitment comes with the satisfactory completion of OCS. This where the rubber meets the road. Yes, you will have to "commit" by your Junior year to what your military obligations are, but by that time also you will have a.) figured out if this is something you genuinely WANT to do and b.) the ROTC cadre would have figured out if you "pack the gear" to warrant being advanced to OCS - physically, mentally, emotionally, and as a leader.
Yes, getting a ROTC scholarship is a great and worthy thing. But you have yet to be tested as to your commitment to a military life-style. A commission is NOT guaranteed; it's largely up to you.