I made the mistake of buying my first road bike on the internet and I thought it was (majorly to small). It wasn't until I went out a purchased a bigger frame (and sold the smaller) that I realized what a dolt I am. So maybe if you think you're on too small of a frame, most of the time you are, but sometimes not.

If my first frame was marginally too small (by about a cm) it handled much better than the too-large.