get behind
US /ɡet bɪˈhaɪnd/
UK /ɡet bɪˈhaɪnd/

1.
retrasarse, quedarse atrás
to fail to make enough progress or to be late with something
:
•
I've got behind with my work.
Me he retrasado con mi trabajo.
•
If you miss a few classes, you'll soon get behind.
Si te pierdes algunas clases, pronto te retrasarás.