I am in an arranged marriage, what should I do?

Im 18, and i just found out im in an arranged marrige. I'm french, and he's swedish, (i know, the circumstances are strange). Hes also 18. Our parents have known each other for a while and they decided it would be a good idea to put us into this. I haven't met him yet, but he comes in a few days. I'm torn because I honestly don't think I could score a better man (from out phone conversation he seems very nice and funny), but I also don't want to be put into a marriage at 18. But I can't say no, because my family will disown me and i would miss my little sister and brother terribly.