You did fine, i can barely buy a 63 for that price.... Also, i believe the reason it recieved a 64 is because of strike. Had this coin been flat,(like alot of Os) it probably gets a 63 imo
I agree with what you are saying about strike. Most of the 1883o Morgans I see have such a flat strike that at first look they look AU. The hair above the ear looks pretty solid except for the scuff on the slab. Here's Apmex's stock photo for MS-64 1883o Morgans. Here's Coinfact's photo of the 1883o Morgan in general