you will find the USCG nav test comparable to the ASA exam, so no sweat. You will find the USCG Navrules exam far more difficult than the material in ASA tests, and getting the 90% requires that you know the stuff cold. I dont think any one class can do this material justice, you need to study/cram/flash cards/sample exams until you are blue in the face. I also recommend the Weems&Plath light rule card for route learning of vessel lights Weems & Plath Light Rule Quick Reference Vessel Id - 190 - BoatersWorld.com
The USCG Deck and General covers stuff us recreational boaters never see and is way too broad to really study, yet study yet alone learn. What you do need to learn is how to find stuff in the CFRs which will be in the room, understanding the types of stuff that are in the CFRs and how to find answers when you otherwise have no clue, is what you need to learn.
PS - if you'd like, you can borrow my Weems&Plath light rule card until you're done...it worked for me...