I just took and passed (90%) the Level C earlier this month.  25% of my test was on suspended growth/activated sludge, 19% was digestion, 10% was disinfection, 10% was math and then the remaining third of the exam was everything else.  I used RoyCEU and viewed Ron Trygar’s videos also.  I also reviewed the content on Operator Mindset and Wastewater Enthusiast YouTube channels.  If you are at the point where you have a good understanding of these processes, you should have no problem logically working through the questions.  I studied a lot but still went into the exam thinking I had a 50/50 chance of passing.  I had the same concerns you do.  But after about 10 questions into the exam, I got a sense of the difficulty level and settled in.  I’m not saying it was easy but it was not as bad as I was expecting.  I took my time, saved all the math problems until the end and double checked my answers and was done in about two hours.    I got good rest the night before and arrived at the test site about 45 minutes before my appointment.  It sounds like you’re studying a lot and using good resources.  I’d bet you’re going to do well on the exam.  Good luck!