Well you said you already have an offer, so they clearly think you are qualified. Is your offer conditional or unconditional? Check the offer conditions if it is conditional. There will likely be a line about your final marks being up to a certain standard when you send them your transcripts, if you haven't done so already. If you are close to the required GPA but not quite there I doubt that alone would completely disqualify you, if you already have an offer. This should all be in the fine print of your offer though.