I was doing the exact same thing--actually the exact opposite, as I'd always turn left, and as billvon explained, it was a sub-conscious reach. The neat thing is that this habit (which wasn't easy to stop at all) helped me get the feeling for a more dynamic flare: Since I could not stop myself from the habit of initially reaching down with my left hand, I eventually just noticed that I could easily adjust to correct for it during the flare:
I would unavoidably start turning slightly left, but I'd notice this as soon as it started to happen and I'd immediately adjust by pulling the right toggle slightly further down and noticing how the canopy would straighten out. This showed me how much room and time there actually is during the landing flare, for all kinds of adjustments, and I got more and more sensitive to the feedback from my canopy--noticing subtler and subtler changes in its flight behavior. Eventually, I stopped turning left, not so much because I stopped having the unconscious reaction, but more because--if anything wasn't straight, or if I wasn't at the right height or anything else felt off, I would immediately make tiny adjustments in the flare--this now happens almost automatically, just like your body automatically knows how to make balance adjustments, if you're walking on the grass and your foot lands on a slight angle, etc.: You barely notice this consciously, because it feels so natural.
The whole thing does get a little more tricky in cross-wind landings when there is some serious wind, though. (and again: I have the feeling that some student canopies just respond a bit more sluggishly, making these adjustments harder to gauge by essentially having a slightly lax interface between pilot and wing)