Its really not an issue - I'd always had guys as my best friends before I went to uni and I still do now, its not as though living with just girls (in your case) is going to change this at all. I've lived in a girlie flat for 2 years and a boy-girl flat for 2 and it really makes no difference at all to the dynamics of the flat, and I certainly don't think not living with guys the entire time has killed my social life involving them in the slightest! As has been said, there is a mixture of guys and girls flats in each building so you'll meet loads of people that way, and then in societies and your course there will also be guys there, obviously!