Hello.
Please ask your question in the Gynecology Expert Forum at:
http://www.medhelp.org/forums/show/103
If you are a virgin and get married, then in is not possible that you cannot please your new husband. If he is not satisfied by you by you giving your ultimate love sacrifice to him, then he will never be satisfied with human sex, and will always be disappointed.
On the other hand, since you are 21, you body has grown from puberty, and your sex organs have grown with you - I think that your vagina will be the right size for having sex with your partner, and giving birth to babies as well!! :-) It will never be "loose", it will always be "you"