Is it normal to have lines on my teeth after braces?

Yes it is quite normal to have that. If the lines/ spots are whiter than the normal teeth, it's because of the enamel that was worn off when you had the braces. If you drank soda, had a lot of citric acid and sugar, than that would be it. But if you did take care of your teeth properly and thoroughly, the lines should wear off at least a little bit, maybe not all the way.