I'm just coming to terms with the fact that I'll soon be making all the decisions for myself and there will no longer be a knowledgable passenger sat next to me in times of uncertainty.
You already had this situation during your solo flights, as part of your training.
As long as you keep on learning, rather than unlearning, in your upcoming flights, and gauge your capabilities conservatively, you will be OK, and self confidence will come.
Interestingly, I was happy when I could start flying alone, and I made a lot of effort into maintaining my currency so as to avoid sitting with instructors again. Of course, I did talk to them, I even had a check-ride due to starting to rent planes from a new place. Nevertheless, I don't even like other pilots joining me either in the right seat. I happily join other pilots in the right seat and enjoy being passanger again, but in my right seat, I prefer another passanger or being empty. Probably because it gives me the chance to learn faster, more, deeper, than having someone helping, yet at the same time preventing mistakes in the first place.
Just make sure you have a little book in your flight suit, where you can pencil down your own de-briefs from your flight - what did you learn, what you should focus on during next flights.