How to Reduce the Size or Bridge the Gap of a Vinyl Floor Expansion Gap
Use a traditional baseboard. If you're concerned about moisture, instead of wood/particle board, get PVC. There is plenty of nice stuff available like this one from Home Depot



You should be able to find one with a just-wide-enough base. If not, use something simpler and add a matching 1/4-round.

You can paint the baseboard the same color as your walls or a contrasting color.