Well, sorry, didn't mean to freak you about your new used boat. I'm sure you'll get lots of different opinions about beginner boats, and you can go out in the M3 and do just fine.
Personally I don't think a creekboat is a great pick for a beginner. It's been designed for running class IV and up kind of water and you'll just be running II and III for a while. I'd liken it to taking a Hummer vs. a sports car out on the highway. The Hummer's great if you need to go plowing through the back woods, but it's not going to perform as nice as the sports car on the highway.
Some might say a creeker is great for a beginner because it's going to be more forgiving when you lean the wrong way or go into the current at the wrong angle, etc. I think it's better to get punished for those wrong moves so you can learn quickly in smaller water how you should be moving the boat through different features. Plus a more nimble boat will keep you out of trouble in the first place.
Anyway, I'd advocate something in the river runner/ playboat category. Wavesport EZ, Dagger g-ride (I think), Pyranha I#, or any of the many others. If you think you're going to be a slow or timid learner and want something more forgiving then the a river runner/creeker hybrid might be a good option like the Pyranha H3.
Just my opinion. I'm not an expert on boats so take it for what it's worth. You've got the M3, go learn how to roll, ferry, eddie in/out and all that, but as your learning you might want to check out some other people's boats.