Hello!! I have been a Surgical Tech in Endoscopy for 9 years. I am now an RN student, and looking to get a part-time job in the GI Lab for some extra money. I love it!! I can tell you a few things.... The first is that there are many types of "Techs" that can work GI. These can include Surgical Techs (they go to school to learn the OR, Endo, and Central Service), Endo Techs that have learned on the job and have specialized in GI only, and CNA (such as yourself!). I am in no way saying that this is all, but these are the only ones I have learned about from the 9 facilities and 4 states that I have worked in.
The other thing that I can tell you to expect is greeting patients, registering them, instructing them on how to change into their gown and placing them in their assigned beds, taking and recording their vital signs, and assisting the RN's,CRNA's, Physicians, and anyone else that may ask. You could also be trained on putting charts together, helping with admission papers or registration, and so on.
As for the procedure rooms.....OMG....jump on the chance to at least get in a room and observe. That way you can better understand what it is the patient is there for, why the preparations the patients go through is important, and can ease you into the idea of working in the procedure rooms. If you love it and have an interest in it...go for as much as the facility you work in will allow you to do. It is a very rewarding career.
I hope this helped. Good luck on your first day!!!