If it turns out the scratch is into the element and you find it does cause flare a time honored repair can be made if you are very careful. The offending scratch can be filled in with india ink with a very fine brush or toothpick. The black mark will simply block out a very small amount of light and prevent any from being turned into non image light. this works even with fairly large chunks taken out of the lens, though it throws the f stop scale out of kilter for exposure settings.
Most times a lens can't be repaired when scratched and this is the only recourse other than making a doorstop out of it and buying a replacement lens.