Formal Do - What to wear? (Urgent help required!)

I've been invited to an Awards Ceremony at short notice (this Thursday!) Problem is, my husband can't remember if it's black tie, formal or what! I'm now panicking as I went into town today and bought a dress:

http://www.monsoon.co.uk/evening-dresses/monaco-dress/invt/75222875/&bklist=icat,5,shop,women,dresses,eveningdresses

Got pretty black sandals and a silvery wrap to go with it, but am now worried that it's going to be too short and thus be a fashion faux pas. Any thoughts would be greatfully received! About 1000 folks going so won't all be long will it?

It is a really nice dress. The fact that it is a shorter dress  means that it will fit in with formal or not quite so formal.

Have a good time ! A few glasses of vino and relax.....

Thanks ladies! Having googled I finally stumbled upon some photos and amidst all the really well dressed people in bow ties and ballgowns was one of my good friends. Have messaged her and she tells me that although there are some very well dressed people, there is a variety of dress, and some ladies opt for trousers. Feel much happier now.

Thank you all