Question about sizing

So I am currently riding a Cannondale, F5 mountain bike. I've tweaked it every which way and it STILL feels twitchy. I feel like my knees and elbows are just too close. It's a Medium frame and I'm 5'8 and I have a 32.5 inch inseam. I'm thinking maybe the bike is just too small? I've heard from other riders that Cannondale's run very small. Anyone have any ideas? The reason I ask is that every time I have taken this bike off road I crash it. It feels awkward to me, I feel more secure on my commuter on uneven ground than I do my mountain bike. That just seems wrong. I rode it tonight for about 25 miles and it just feels small.:confused:

Take it to the LBS and have them look at fit. They might be able to make adjustments, or change out your stem, that will make a big difference in your ride.

. . . or they will confirm that the bike is too small and you can exchange it, or sell it on ebay, and get one that actually fits right.

You want your bike to be comfortable, and you definitely want to be able to handle it so that you don't keep crashing.