My screen is covered with purple streaks/lines, what do I do

During class today i noticed my phone had a purple smudge color at to top left corner of my phone, but i ignored it thinking i got pen ink on my phone again. Well the end of the day comes and i come to see that my phone is covered with purple streaks all over my screen. I didnt drop it on water or put too much pressure to my screen. Although my screen is still responsive and everything still works. the purple lines are still there. what do i do?