If I had to guess I'd say you you used the backward loop (or single) cast on. That one is really only good for casting on a few stitches. Long tail is the most popular, but the knitted cast on is easier to learn if you're new.
Here's the backward loop to see if that's what you used.
http://www.knittinghelp.com/apps/fla...ayer/play/35/1
Here's the main page of cast ons.
http://www.knittinghelp.com/videos/cast-on