What if i dont appear for my improvement exam?

So i applied to appear for improvement exam for a core subject from a previous semester and just realised i cant do it anymore due to other commitments. Im having trouble getting it removed by college admin. Many friends have told me if i dont go to give my improvement exam, my grades will be same as before and i wont be marked an ER due to absence. I want to know how true this is. Please help.