Yes, they are interchangeable. Most commonly, they're used in the simple past tense. I was qualified for the job, but when it came to the interview, I screwed it up. I was qualified for the job, but when it came to the interview, I blew it.

You can use it in the present tense, but it is almost exclusively used in the past.

Not to split hairs, but I think it is possible to use 'you blow it' in the present tense. "You blow it every time you talk to her."

The first one is only ever used in past tense ("You blew it."), but otherwise they are sometimes interchangeable. The nuance is a little bit different though. Usually, to screw something up means to mess it up with a mistake, while if you "blew it", it can mean that it was a simple failure.