Nuvaring and pregnancy?

So i was prescribed Nuvaring back in November 2015 and the doctor said rather than removing it after 3 weeks & having a period, I can just use it continuously and take it out & replace it the same day/time each month (for me, the 10th). So, that would mean replacing it every 30 days. But upon research, I found that you should be replacing it every 28 days. So, i'm now worried i might be pregnant. It's February and I just missed my first period and I had unprotected sex. I'm worried that replacing the ring every 30 days rather than 28 messed me up. Should I be worried? Is the ring still effective when I replace it at 30 days instead of 28?