Biology isn’t that simple. A person can have one fewer sex chromosome, monosomy, one extra, trisomy, and many extra, polysomy. In fact it’s starting to show that a significant minority of people have trisomy 47 (the name for having one extra sex chromosome) but live perfectly normal lives because those extra genes are suppressed. You could have an extra x chromosome and never know it, does that exclude you from being a man or a woman? Which brings up the topic of gene expression and epigenetics which is even more complicated. If you’re looking at science to give you a certainty about sex and gender you’re in for a long search.
I was looking for this comment and I’m glad someone got this one in promptly.