Its just the leaf growing, some parts of the leaf are growing faster which causes the twist. It will all even out soon. Id add more dirt upto the brim to help support the stem. Any part of the stem you bury under dirt will soon grow roots. When I plant seeds i only fill the pot about 25% so that as the stem stretches I can add more dirt. Once it stops stretching the dirt should be about 1-2 inches from the first leaf. From the pic it looks like yours is about to stop stretching.