Can using white strips make fluorosis worst?

No: There is very little benefit from over-the-counter whitening products anyways. A professional whitening from a dentist will whiten teeth even with fluorosis or tetracylcline stain, however, the whitening trays will need to be worn for a longer period of time. It certainly won't make fluorosis worse.

Definitely, no: Only a child may get the enamel fluorosis if he or she gets too much fluoride during the years of tooth development. It is not possible at your age.