A few things....first...nothing wrong with trying electrics out as your first. One thing the hobby shop neglected to tell you is that new nimh battery packs need to be cycled at bare minimum a few times before the cells in the pack get their peak power and longetivity. Always fly these packs right off the charger. They should still be warm. And, if you hand launch, give it a straight sturdy toss into the wind. Some models require a strong throw, let the plane drop a bit and then feed up elevator but not violently pulling back on the stick. What you did was to stall the plane and thats why it nosed down.
My opinion, majority of these rtf's don't have enough power out of the box, are cheaply made and just don't fly worth a crap. If you want to learn to fly, I'd go with at least a 3 channel machine. Multiplex makes a model called an easy star which flies nicely. Since the motor is in the back of the cockpit/canopy/pod, no broken props if you land on the nose. There are quite a few others that would fit the bill pretty good.

Dave...