I just used a non-name brand teeth whitening kit and I have white spots on my teeth?

I just finished using meijer brand one hour teeth whitening kit and all it seemed to do was the make the spots on my teeth that have weaker enamel, like the bottoms, be super white and the rest is basically the same as before. What do I do?! Like how can I fix it?
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It could be because of a few reasons. Go see a dentist.
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