I wouldn't go right to a 3gal I would go to a 1gal 1st. Make sure it is kinda dry and just put it upsidedown. Make sure to stradle your fingers around the plant to protect it. Oh and make sure you put new soil mix (a good soil) in the bottom of the pot you replanting to. about as full as you need to bring the plant up near the top. then just place it and fill around it with with more soil. then water alittle. If the plant is root bound I have heard to gut a few cuts in the roots to get them to grow outward but not sure about that.

You should still have some time before you need to replan. a few weeks I would guess.