Your body will not feel noticeably 'loose' to him. You can act frightened and virginal if you feel you must, and he will almost certainly not question it. Not all women bleed on their first intercourse. It is also possible to fake that, if the situation is dire. Do you really think your fiance would be upset if you were not a virgin? That is different in different countries, some men don't care if she is, and in other places, the woman seems almost to be in peril of her life if she is not a virgin (though it doesn't seem to matter if the man is a virgin). If you are in a place where it is dangerous not to be a virgin, don't worry he cannot tell by the size of your vaginal opening.