sorry to sound gross, but could just be some congealed cervical mucus or leftover DTD evidence - especially if no tinge to it. The plug can replenish, so if it wasn't much, I wouldn't worry too much, just mention it at your next check-up or ring a midwife (depending on your care preference) and just check-in if you are more comfortable with it.

But, I don't think it sounds like the whole plug, but it might be a little bit KWIM?