"It's up to you!"
This is a rather unnatural English translation for this, imo. I've learned 随便 in my courses before, but translating it this way is a little opaque to me.
No. 你随便 is not an equivalent.
We can say 随你便! as an alternative, but not 你随便.
你随便, not with an exclamation mark, can be used when we receive a guest, but leave him/her doing whatever he/she likes, e.g. someone walking into your bookshop to find books, a schoolmate coming to work on your computer, etc. So it's pretty much like "Please feel free."
随便你 and 你随便 may not be equivalent in Chinese, but given the definition you describe, they both sound like they could be translated to the given English translation -- the English translation given is very vague, imo.
But I suppose it's probably not something that would've been learned at this point in the course.