I accidentally added the same w2 twice and it messed with my return even tho i deleted it once i realized i made a mistake will i get it back it was about 300 dollars?

i realized i had put the same w2 in twice but removed it it said i had already submitted my taxes but i hadn't done anything but check my return and made sure everything was in check and i realized i had put it twice but it still took 300 dollars off my return i tried clearing the information and starting again but it said i had already filed and couldn't change anything when i didn't file anything yet