If I understand correctly, you now think you should have cut back the stems closer to the soil. If so, you can re-cut at any time. The new growth on those stems will probably survive your attempts to propagate them. Next, time prune all the way back to within a couple of inches of the soil right from the outset.
The thickness of the stems depends on the available light at the time that part of the cane is first growing. The original canes were grown in ideal greenhouse conditions with optimal light, which is impossible to duplicate in your home. If you improve the available light, new stem growth will be thicker going forward.
