What major did you apply for at UMD? What did your guidance counselor say when you were rejected last year? Were your grades/test scores/something else significantly lower than those of students who were accepted from your high school?
Your best bet for transferring into UMD is to complete the MTAP at a community college. https://www.admissions.umd.edu/apply/admission-requirements/transfer-applicant-requirements/maryland-transfer-advantage-program
That said, UMD accepts a fair number of transfers from other universities each year. Go ahead and apply this year if you want to.