Today I had my NT scan at 12 weeks 1 d but measured 12w 6 d is this normal and okay? What would cause this?

Yes. It's normal for a first trimester ultrasound to be different by 5 days and still be within the standard deviation of error. A fancy way of saying, that yes, it's okay that these 2 different gestational ages were given. Your doctor will tell you which is the date he/she is going to go with for the remainder of the pregnancy.
Normal. Ultrasounds in pregnancy can be up to a week off of your dates. Your OB will consider another ultrasound later for comparisons.