If you take the plant, wash off all the soil, and spread out the roots, you will see that these roots will OVER-FILL a 3 gallon pot NOW. Why can't you plant it in the ground and put your trellis behind it?

This vine is a very agressive grower - it need room, and lots of it!

For a 1 gallon plant you will need about a 10 gallon pot - for good growth, in a year you will need to bump it up into a 20 gallon pot.

Plants just do better in the ground, where they can put down feeder and water roots and fend for themselves.