You can’t have it both ways. The school doesn’t want to be your back up prom date, ready to take you if a better offer doesn’t come along. They want a yes or no based on what they are offering. If you aren’t ready to commit, then you have to let it go. If it is still there in April (probably won’t be), you can try to get it back.
I don’t see this as different than ED. The offer is made, and you can take it or leave it without knowing what else is out there.