I'm thinking that there is some great luster that the image is not showing. I'll guess it got a 65 but that mark makes me call it a 64. The lighting could be catching a tiny scratch? It could be a 66. Tough image. I'm betting the field, 64 to 66. I like the coin. I'll bet it looks really flashy in hand.
There is nice luster on this, most is hidden by the bright light I used to take the photos, it is probably the brightest luster of any morgan I have. The scratch looks about the same in hand as it does in person, looks like a mark from being in the mint bag with other coins.
Just to compare, this coin did NOT get a 66 (twice): https://coins.www.collectors-society.com/WCM/CoinView.aspx?PeopleSetCoinID=1653904 Given the gash on the neck of the OP's coin, would you like to reconsider your grade?