Ankles are a tough call - sprains are more common but with all kinds of small bones you never know. Since you said you 'rolled' your ankle, I'd be inclined to think it was a sprain but I'm not a doctor so don't listen to me!
Your best bet would be to get to your primary care physician so he/she can take a look at it and order x-rays to find out what's really going on.
I'm so sorry your ankle is hurting. At this early stage, stay off of it, elevate it, and wrap an ice pack around it. In fact, if you have a bag of frozen peas or corn, use that and an ace bandage to do a compression wrap. If you can, take some over-the-counter NSAIDs (non-steroidal anti-inflammatory drugs) like Aleve, Advil, Motrin, or Bayer.
Good luck - and go see your doctor soon if it doesn't get better.