How do I fix internal screen marks on my MacBook Air?

The linear and parallel nature of the big marks suggests physical damage to me, like something was left on the keyboard that was not removed before attempting to close the lid. That could cause that type of mark, and would not be covered by warranty.

Other than that, display defects are very hard to diagnose in an end-user forum setting like this. Apple needs to evaluate but they do not participate here. If it does not qualify for warranty coverage, prepare to hear a big estimate for fixing.

Your display is one sealed unit. Should any single part of it be damaged, the entire lid assembly must be replaced. We cannot quote costs here but others with similar issue have posted that the parts + labor cost of an Apple repair start at about US$500 and goes up with screen size.

You can make an appointment at Apple and have that MBA evaluated. The only way to know if this is something that they will fix is to ask.

You can make a Genius Bar appointment for hardware/software service and support using this link: Make a Genius Bar reservation - Apple Support

Customer Support (800) MY–APPLE (800–692–7753) or on line /getsupport.apple.com/ 

or call AppleCare Support at 1-800-APLCARE (800-275-2273)