Oh boy this puts me in a conundrum. I want to put one in pot so I can bring it in to the house but it's only half the diameter I want. Oh well I guess I'll have to keep it out another year.Sure, if you are happy with the diameter of the trunk, move it to a bonsai pot.
Depending on species, most trees do not thicken much once the roots are confined to a bonsai pot. Case in point. I had a pomegranate cutting that I kept in a bonsai pot for its entire 38 years. It took 38 years to go from less than a pencil diameter to just under 1 inch diameter. If it were in the ground, it easily could have been 6 or 8 inches in diameter.
By the way, some trees increase diameter in pots better than others. But in general, don't confine the roots of a tree a bonsai pot until the diameter of the trunk is reasonably close to the diameter you want.
I had a few nights when temperature was below freezing. That's why I had to bring it in. You are right the mix is wet. When I potted that in June it was super hot and I often had to travel, I had quite a bit of stuff to retain water while I'm gone for extended period. That mix worked well for me in the summer. Now that I got it inside, I use a water meter to keep myself from over-watering it. Even if I don't put it in a bonsai pot, I will still repot it next year to put it in a dryer mix.Your mix looks super wet. Bougies like to dry out a touch between waterings. In your zone, you should not need to bring it indoors. Bougs are fine into the 40's at least and lower depending on variety.
I would leave it be for now, cut it back to the lowest leaf nodes whenever bud break is for you then give it as much sun as you can till July and see where you are at.