The chances are very very (very) slim. The ring is meant to protect you from a fertile man ejaculation inside you right at your most fertile time and on this day you had a very low chance of being fertile. In other words, the ring will protect you EVERY single day of your cycle as long as you use it as directed.

Your period can be irregular for many reasons. If you want to put your mind at ease, do a pregnancy test 7 days after your missed period and follow the instructions EXACTLY.