Personally, I prefer text, and practically every chick I have been with seems to go along with it.
If she has given up the digits, then forget about asking her in class (could be embarrassing for you both) and just do it by text.
Be definite in your plans and not wishy washy. If she is interested, she will say yes.
And remember.
Alcohol = Sex. Food = Sleep.
PS - [added after you deleted your thread text] - are you gay? Just fvckin' go for it and good luck.