I think they'll probably dock just 1 mark, don't worry too much. I don't do America (I do Elizabeth, Cold War, nazi Germany and warfare) but generally they look to give as many marks as they can. Apparently they used to be really strict and start with full marks and take away as they saw mistakes, but now they just start from 0 and give marks for good points, even if you do make mistakes.
So yeah, don't panic for no reason. \(^-^)/