Hello,
You should use a back up protection for the first week after insertion of Nuva ring. Chances of pregnancy are less in your case. If you are apprehensive regarding the status of pregnancy then you can test for it., Most home pregnancy tests that check urine beta-HCG are sensitive to 20-25 mIU/ml of HCG. The test can be positive anywhere from about 2-3 days prior to a missed menses to 4-5 days after, but usually it should be done 7-10 days past your missed period.
Otherwise you can get a serum HCG also done which is more specific than urine pregnancy test.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
This vaginal ring is supposed to "work" properly for 3 weeks in a row.