Is there an American English expression to say:
to pull one's socks up
?
For example in this sentence:
You only have got two weeks now till the exams start and you're going to have to pull your socks up if you want to pass, otherwise you're going to fail.
"Pull your socks up" would probably be understood as an idiom in AmE, but it is more common to say "It's time to straighten up and fly right!" Or, used in your quote, "You've only got two weeks until exams start, so you're going to have to straighten up and fly right otherwise you're going to fail."