You may have registered your marriage, but have you gone through
the solemnisation ceremony in the presence of the Justice of Peace
and witnesses yet? If so, under Singapore law, your "boyfriend" and
you are considered husband and wife. And under Singapore law, any
party could apply for annulment of the marriage on grounds of
non-consummation.
It is commendable that you respect your body, but you have to try
to understand the feelings of your "boyfriend" as well. Have a good
calm talk with him. He is probably frustrated and getting teased by
his buddies, so explain to him nicely that you are not ready yet,
and want to save yourself for
him (emphasise) on the big night. If he is all geared up and
ready to have a go at it, just try to help him cool down a little
through some "physical intimacy" without sex first. And if you
still don't know what to do for "physical intimacy" without sex,
you probably need to do some reading up. 
Don't worry. Your "boyfriend" is unlikely to nullify the marriage
just because you didn't give him sex before the big night. He's
been patient long enough, a few months wouldn't kill him.
