"There is a "X" next to my module instead of a check mark"
This "X" is an indication that you did not reach the end of the lesson (think of it as a bookmark, holding your spot so you can come back). Please click the green play button for that lesson and continue the lesson until you get to the final slide that instructs you to close the lesson.
If you already have a green completion check mark, you can either ignore the "X" or click on the "X" and cancel the module. Your completion check mark will not be lost.