Everyone goes into repeating a subject with the determination to get a better score, but very few stick with this drive. I believe that a lot of my friends who have repeated subjects found that it became mundane, tedious, and at times you over estimate yourself, believing that doing a year suffices as a reason to procrastinate studying it hence not needing to try hard during the year.
I'm not saying that it's not possible, i'm sure that if you want it enough you can do it, but i think that it is strenuous on yourself and can be a waste of time. The reason people do subjects early is to get it over and done with so it seems a bit counterintuitive to repeat it in my opinion.
You seem content with the score already. Think about all the time and effort you can dedicate to the subjects you have in year 12 now that psych is done. It's understandable that you want better, but i doubt that redoing it will be beneficial for you. It's not guaranteed that you will do better plus if you repeat the year and get a ss that's just a few points higher, do you think repeating the year would have been worth it?
I did psych in year 11 and got a ss of 41 which was fine with me however i did contemplate repeating it. I'm really glad that i didn't though because it would've jeopardized my other subjects and caused me enormous stress. I highly advise against it, but if you really think you can do it then it's up to you.
Also with doing psychology in uni, just do well with your atar. The atar gets you into the course, not your psych ss