You aren't alone in being nervous. One of our most hardwired survival instincts is that we cannot breathe underwater, so you shouldn't feel bad about your fears.
In order to be more comfortable this time around, I suggest that you go slowly, step by step with the most patient instructor you can find.
When my wife decided to get certified, she took the course from the local college, as part of their continuing education program, because it had higher credibility. In reality it was taught by an LDS owner and his staff, but that's beside the point. She came close to dropping out at least 4 times during the pool sessions, but was willing to keep trying untilhe had her final break doing the free flow breathing excercise.
The only reason she's diving today is that her instructor called me and explained that in 20 years he had only one student drop out and that was years ago, and he'd do anything not to have a second. After lots of handholding and some cajoling by both of us she went back and worked with one on one with a patient trust inspiring instructor who took her through each problem one at a time.
That was about 7 years and 600 dives ago, and now she's a virtual fish.
The point is that if your fears can be cleared away one by one, you'll find that you can do this if you want to. What you want to avoid is trying to bull your way through and being overwhelmed when you hit a snag.