The only people I have ever known that had a pregnancy after the surgery didn't pay attention to the fine print and were having unprotected sex before he got the "all clear" test... not so smart.
My husband and I have been safely using his cut pipes for YEARS with no incidents.
If it makes you feel better grab that test... but more than likely you are just experiencing a slight hormonal shift and your period will show up soon. I know that can be scary for someone who has always been very regular. I guess I'm lucky in that I've never been regular at all, so any lateness or missed periods never fazed me for even a minute once my husband got his "all clear".