The invite was sent about a week ago so it's probably buried pretty deep in your notifications.
Here's a handy link that should be visible to you (and other users that have an existing invite).
imgflip.com/stream-settings?stream_name=Everyones_A_Mod
If your not interested, that's fine you can remove yourself, but it's possible that another invite might come on it's own down the road. If you're not sure right now, perfectly fine to leave it there and think about it.