Unfortunately, you do not get to pick up where you left off with Honors College, so to speak.
Admission to Honors college is tied in to your incoming freshman application/admission status. If you do not accept it, you forfeit it. If you are not happy at the other school, you will have to reapply to Maryland as a transfer student, and all rules for transfer students apply, including housing http://reslife.umd.edu/housing/transfer/
There is a small chance you may be invited to Honors College again as a transfer applicant, IF space is available, but it would only be to University Honors, not any of the other programs within Honors college.
Another way to get back to Honors college would be through Departmental Honors, which is considered part of Honors College. http://www.honors.umd.edu/admission-transfer.html
Something to consider…I personally feel that it is better to be a the top of the pack than at the bottom. You will not only experience greater success, but you will be eligible for more opportunities. If you were waitlisted at this other school, I can only assume that you are not top of the pack for them. The fact that you are already expressing concern about not being happy there may be something to consider before giving up the red carpet that Maryland is offering.
However, whatever you decide, understand that it is not the school that makes you successful, but rather what YOU do at the school that you chose. If that is your dream school, and that is what will make you happy, don’t go in with fear of not liking it, but rather with the excitement of living out your dream and make the most of it!
Best of luck in whichever path you choose to follow.