as long as it doesn't expand, likely nothing. The plant will be 10x more robust in a week.
is it bumpy and kinda hard (as opposed to growth on it that rubs off)? that can be normal. my lower stems aren't so pretty all the time.
now, if it rubs off or has a smell etc.. that's microbial growth. Again, i'd wait and see if it expands in teh slgihtest. it'd be a sign of overwatering -- never reaching a dry time to reduce growth and help plant fight it off etc. But, it sure doesn't look like the case.. looks perfect in picture how soil is around it.. clearly done right.
so, 80% sure you are fine... definitely don't do anything yet that could cause more problems than it solves.