This won't make your pill any less effective.

And don't feel silly, it's happened to the best of us!
You have two choices here -- you can either continue the pack as normal and end one day early -- meaning you need to start a NEW pack one day earlier, or else if you are off the pill eight days you'll need back up for the first seven days back on it. Your other option is to get a new pack of pills, take a "replacement" pill from it to replace the sunday pill you took when it comes time and then label that pack as "extras" and keep it on hand for situations like this.