I went through the AFF course at Raeford including the tunnel time at ParacleteXP. I'll second what's been said: You'll probably be all over the place in the tunnel and if you're anything like me you'll be frustrated beyond belief at your lack of control -- I'm one of those type-A perfectionists that wants to be able to do everything perfectly. Heh.
That being said, once I was actually jumping I was very comfortable getting stable once I was out of the plane. I think the tunnel really forces you to be much more precise with your body position. Plus, the tunnel is a lot of damn fun.
The crew at RPC is also amazing so that helped a bunch, too. The AFF instructors and coaches are really focused on making skydivers out of their students. Even on the busiest of weekends with fun jumpers, tandems, and everyone else coming through they'll make sure you get all the instruction and jumps that you want. I'm really glad I found them! Now, if my back would just heal so I could get back to jumping ...