A student of mine had a similar habit. The previous aircraft he had been flying had had a flat (horizontal) glareshield coaming and he was subconsciously replicating this by aligning the angled B737 coaming with the runway resulting in slip/drift every touchdown after a nicely flown approach. Might be worth a look. As the other posters have said, look well down the runway during the flare as well.
Good luck with your training.