my mucus plug came out. does that mean I'm going into labor?!

If it was super bloody then yes. If not it's a maybe, but it is getting closer.

Not always. You can lose parts of it and it can regrow like when it happens to women in the second trimester. If your losing it and have your bloody show, contractions, or your water breaks then you might be starting labor! But just losing it doesn't always mean labor.

yeah a little bit came out

It could but it also couldn't.. for me, I was in labor and it was coming out. for others they had parts of it come out and still wait a while for labor.