Can I fix my worn out charger port?

If it indeed a "scratch" the warranty should still be valid. However, if this is really a crack, then you're correct that warranty is void. This charging port is soldered so you'll have to microsolder the replacement. If you've not done this before, then I don't suggest that you try it on this phone. Take it to a local repair shop and have them fix it for you. If you can't find anyone locally, contact me and we accept mail-in repairs.