Yeah, don't get too worried about it - you have other boating skills, the canoe skills will fall into place fairly quickly.
I was in an almost similar kind of place 2 years ago - I'd had my Ocoee a while but not paddled it for a couple of years and then only on flat moving water.
Tried to paddle a grade 2 rapid and swam right off the cuff which shook my confidence quite a bit. Then did a little flat water training on Loch Lomond until I was reasonably happy with my balance and got reasonably close to rolling it.
Next WW trip was in a rental Whitesell Piranha in the Grand Canyon - at Lees Ferry I literally had no idea if I was going to be able to manage it in the rapids (I had figured that at 14' it was going to handle more like a trad than my Ocoee). 200 miles later, I think I'd had 7 real swims, 1 swim trying to surf a wave and 1 swim on flat water trying to get comfortable, and 2 portages. After a couple of swims early on (none on day 1) I was able to relax, stop worrying about swimming and just learn to paddle the boat.
Your practise session is what has caused you concerns - OC1's are not stable like trad canoes, you don't just step in, you get on your knees right away or it will tip over. The boat reacts much more to little movements and you will take a little while just to develop a feel for that - the same way you can confidently walk on the side tube of your raft now allowing for the movement as your weight transfers onto it, but when you first tried years ago you probably almost fell off. Wearing your jeans instead of a drysuit really screwed with your mind because you knew that falling in could get to life and death (well certainly very uncomfortable), if you had been in your drysuit and had turned over you would probably have shrugged it off and tried again. Going out in strong wind was a mistake, all canoes (except low decked ones) are strongly affected by wind, it pushes them around making it difficult to get a feel for control and it can de-stabilise them too. Nothing worse than a committing to a cross bow stroke and having the bow blown round towards the paddle trapping it under the boat! But you can put all that behind you.
Make sure you have some good buddies on your first river trip, and wear your dry suit - you will probably fall in. You probably won't fall in on the crux of the the first rapid, you will fall in somewhere though either because you put on too much edge crossing an eddyline and dipped the gunwale (I still do that!), or you hit a rock that threw you to the off side, or some other niggling little thing that had nothing to do with the main focus of a rapid! You will have some moments where the flow is faster than your brain and you freeze between strokes trying to work out what stroke will work best next, and when/where to plant it (I decided that it is probably better to just commit to the wrong stroke than no stroke at all, that way I have the ability to brace on the wrong stroke). You may be lucky enough to find a drop that works best for someone who paddles on the other side to you (lefty line or righty line?) which will give you some real thinking to do!
I'd say dress for immersion, expect a few swims and get used to self rescue (OC1s are easier to tow if you turn them the right way up straight away), once you have done a few it ceases to be a source of worry and just an annoyance which spurs you on!
Getting used to the way the boat moves on the water - I had a disagreement with someone at Lava kind of stemming from that. I had got used to the way the boat bobbed as I got into it (9 or 10 days in the saddle), I had scouted Lava and it looked bad at the level so I needed to ferry to the far side to portage or line it. One of the kayakers wanted to help me get back in my boat, I was trying to politely refuse assistance because having someone else holding it changed the way it moved as I climbed in, and at that point I really didn't want a wobble as a result. They on the other hand were probably even more concerned than me to make sure I got in safely, but faced with a bit of a paddle upstream, long ferry and even longer portage/lining I really wasn't about to make time to explain to them why they could best help by not touching the boat as I got in. To be honest I would have forgotten about it almost immediately, but the kayaker got upset that I didn't say thank you for what they intended as help, which was actually a hindrance - well why would I?
18 months on, I'm pretty happy on grade 3 in the Ocoee, run a fair bit of grade 4 too, mostly waterfalls so far. I can sometimes roll but still swim sometimes. For years as a kayaker I was uptight about swimming (very rarely did), paddling OC1 has made me embrace it!