You'd be better off with a 30 amp, but since 20 is it for this trip you can make it work. If you're running the A/C, keep lights to a bare minimum. If you use the microwave or a coffee maker/hair dryer/similar, shut off the air until you're done. Guarantee you'll pop the circuit otherwise.
We have our TT plugged in at home 24/7 on a 20 amp dedicated circuit. It's only for the air + the frig.
If you don't already have one, strongly suggest you make a stop at Lowe's, HD or hardware store for a plug-in volt meter. It's likely less than $10. Plug it into the power pole before you hook up to be sure there is sufficient power coming in. If incoming is good, when you get set up, plug it into a very visible receptacle so you can easily notice any changes. We have had ours since our HTT days and now the TT and on our last trip it was toasty hot and lots of big rigs in the CG drawing a lot of the power. We didn't pop any circuits, but watched it closely as it was getting down close to the red area on the meter. DH got our 50 amp adapter and swapped us to 50 and we were much better. If you see that it's in the red, shut off the A/C. Not enough power coming in can cause big problems with your unit.
For future trips, if possible, get 30 amp. Might also invest in a 50 amp adapter for "just in case" times. Keep it in your storage area.
Happy Camping!