How bright is your light?
A lot of rotala will bend over, particularly in high light, and try to root back into the substrate. Planting a bit closer together helps as plants will reach up for better light access (just don't pack them in too close or they lose bottom leaves).
If you let them go like that for another week or two and then trim and replant the tops between the rooted bases, the increase in plant density should help a lot, especially as the bases push out side branches.