Talk to your immediate superior about why you were denied, then discuss available options. You want to be sure that the disqualification was not due to error or misunderstanding.
If ROTC denies your clearance for security you can enlist, rather than commission, and pursue a similar line of work on the NCO-Enlisted side of the armed forces.
Many times when you are denied a clearance it could be based on mis information. You can request to speak to someone about the reasons why you were denied and if you are able to fix them or correct the mistakes you can re apply.
