You are doing it correctly. That's how most doctors count the months. You are 6 going on 7.
Your 7 months and 3 days. There are 4 weeks in a pregnancy month
A lot of people count pregnancy in a 10 month set. This is going by 1 month= 4 weeks instead of the traditional 30-31 day month. So while going by calendar year you are only 6 months, you are actually 7 months counting weeks. Make sense? It was really tricky for me too my first pregnancy.
I count like you do, so I agree with your calculation. I'm 13 weeks so I say I'm 3 months and 1 week.