Don't worry about it. The lettering on the bottom part of the front is also machine-readable, so if the magnetic part on the back doesn't scan they can still scan the front, and once the information comes up on the system they'll see that it matches what's on the card.
However, if the damage is very bad, the immigration officer at the POE might type into the system that you have a damaged card and tell you to get a replacement before you travel again. Which means you'll have a problem if you travel with it again after that. And some employers might not want to accept a damaged card. But if you have a Social Security card without the employment restriction wording on it, you can show the employer the SS card + driver's license or state ID instead of the GC.
