Don't worry, dude.
You're far from being the only hetero male who's wondered what it's like to be on the receiving end. I suspect that most guys wonder and secretly want to try it.

A few words of advice, should you wish to try it again:

-lube. Lots of it. Put some not only on the toy and outside your ringpiece, but use your fingers to put some inside you as well.

-warm up a little before going for the full thing. That means that she (or you) should start out with a finger or two and massage the sphincter a little from the inside. Then take it slow on the initial insertion- she should stay still while you move backward onto it, and take it slowly. Alternatively, you can straddle her and take control of the initial penetration that way- after the first few moments of it, you can switch positions and she can go to town and it won't hurt as the muscle has already been stretched.

-the size of the toy really does matter. Apropos to the QOTW: pay attention to what comes out of you the next time you drop a large log. You don't want to use a toy that's larger in diameter than that.

-if you're going to do it, make sure you've recently taken a dump to clear out space in there. Otherwise you're going to have a lot of santorum afterward, and it's going to be uncomfortable having your innards compressed, so to speak. (Google for the word "santorum" for edification.)

And how do I know all of these things? From reading a lot of hilariously strange things online, mostly. www.sensibleerection.com tends to have some rather odd conversations take part in the comments...
( The Resident Loon Not a demographic. Do not measure., Fri 28 Mar 2008, 19:16, Reply)