It sounds like I'm at about the same experience level as you are. I'd only done a couple of dives since I was certified in 2005, so when I went on a dive trip over the holidays this year, I re-took an OW class. My buddy was taking OW for the first time, although he is very comfortable in and under the water.
I was feeling
very glad to have instructors right with us.
Then came a day that there wasn't an instructor available (we had been going to take AOW), and... unexpectedly, we were on our own! The trip was to be a boat trip out to a relatively shallow reef (35'), so from that angle it was not going to be complicated. The boat captain was one we had been out with on our previous dives (he did not get in the water though but stayed on the boat).
Okay.... nerves!
But you know what? As it turned out I actually felt better about it in many ways. Not "better" as in "I wish I'd never gone with an instructor," but just that it was a great experience. The thing is, on the dives with an instructor, I was busy paying attention to them and following them, and that in some ways took the place of some of the thinking for myself. Also, you need to keep to the instructor's schedule, so you go in when they do, and dive their dive. Not that this is a bad thing, of course.
Once we knew we were on our own, and we got down to making our plan, I started to feel good about it. We talked over how we wanted to make our dive, how/when/where we would descend and ascend, when we would turn back to the boat, what we might want to practice, and also went over hand signals, etc.
After the boat got situated, we took our time doing a buddy check, made sure we were both comfortable, and then... we were off! Both dives were great experiences, and although I was at first disappointed and nervous that there wasn't someone to go with us and instruct us, it turned out to be a great experience and a real highlight
Like you, we went on a dive that was relatively simple.
So although I can't speak for you, or from the position of expertise, I just wanted to give you my perspective, since we're in a somewhat similar place in our diving.
B.
Me:
May 2005: OW certified with two lake dives cold, murky water
July 2005: Two boat dives in Key Largo with very experienced buddy
January 2008: Two boat dives in Marathon with DM who was specifically my buddy (not the group guide)
December 2009: Took OW course again in Florida Keys with buddy who was taking it for the first time, including four ocean dives for checkouts.
One night dive with group guide
Four independent dives with my newly certified buddy
Looking forward to more