I just bought a new compound crossbow and I fired it about 20 times already. It was well waxed as soon as I bought it. I noticed today while shooting it that the middle section of my string that makes contact with my bolts nock looks slightly worn already. My strings main color is green and I can see a tiny bit of green exposed through the protective black wrap right where it would contact my nock. Should I be concerned or is this normal wear?