I understood you to say that you do not have a rash. The only symptom is the untanned skin. Is this right? Does it look like this?
If so, the over the counter antifungal treatments should kill the fungus pretty quickly. You posted this a week ago. If I had been treating that long, I would suspect it is dead. The white will not go away until you tan it.
If it looks like this
it can also be tinea versicolor, but it will take longer to treat and you should not tan until the rash has cleared up completely and the skin has gotten smooth.
Good luck.