Looks like you've got the shape of the upper saucer, the impulse engine, and deflector housing down nicely!
As for the rest of it, it's good for a start, but if you're going for accuracy, you'll want to redo the deflector dish, bridge, underside of the saucer, and nacelle grills. I'd also add polys to the nacelle pylons to give the edges a more rounded appearance. Oh, and you forgot the three extrusions on the bottom of the nacelles, behind the bussard collectors.
I'd be happy to give you tips and reference images if you like. Just send me a message on WLM. Again, good start.