If the stem of the plant continues to come in nice and thick, you should be good. If it starts to grow out thin and spindly, then it's not getting enough sun and/or nutrients. Generally dragonfruit need ~20lbs of plant matter to fruit (I've heard differing weights given, so take with a grain of salt). Having it top and start to hang down your scaffolding also helps. They get very heavy, so you may need to brace what you have to keep it all upright. Nothing worse than to wait 18 months for it to fruit only to have it topple over and break.

Mine took about six years, but now I am finally getting fruit. Mine is in a bigger pot, just because I have poor soil, but it is so large now that I will not consider repotting it. If you have appropriate soil, transplant it into the ground as soon as you can, assuming you live in a relatively frost-free zone. I have more trellis holding mine up, but I also put it where it can prop itself up against other plants. This is not an easy plant to move, once it gets very large.