I agree that you need to use a backup method of contraception like condoms for the rest of the month. And it would be a good idea, like Clysta said, to test in two weeks.
It is possible, yes. With NuvaRing, you need to use condoms for a month for it to be fully effective. However, you are definitely playing with fire. It makes no difference if you ovulate a few days later, as sperm last 5 days on average in the female body and 7 in perfect conditions. While calenders are helpful, they are by no means exact. It's safer to assume there is no safe time. You need to wait 2 weeks and take a pregnancy test with first morning urine.
I'm guessing your cycle started on the 26th, which was last monday. Most women don't ovulate on cd7. It really depends on how long your cycles usually were. Also, even if you were pregnant, you wouldn't be experiencing any kind of symptoms at this point.
I think cramping is pretty normal with the nuva ring, but I think you should consult the papers that come with it or visit the site and double check. I didn't use the ring long, so I can't really remember all of the side effects that I had, because I quit due to being allergic to it. When in doubt, call your doctor.