You can use "screw up" and "mess up" interchangeably. For example: "I screwed up on my test. I got a 56%" "I messed up on my test. I got a 56%" They are the same, but I think that "screwed up" is a little more informal. Ruin is a little different. "I ruined my test" sounds a little strange... Here are some good examples of "ruin" : "Today I failed my test. It ruined my day." "Relying on alcohol will ruin your life." "My dog jumped on my and ruined my shirt." Hope this helped. :)

I just want to add a few things. 1. As the others have said, "ruin" is not really the same as "screw up" or "mess up." It's not the formal version of those words. Some formal words that mean the same as "screw / mess up" are "botch" and "bungle." (But the difference is that botch and bungle require objects.) 2. "Ruin" always needs an object. I ruined the cake. You ruined Thanksgiving! 3. "screw up" and "mess up" can be used with or without an object. Remember that the normal rules about objects and phrasal verbs apply. Specifically, if the object is a pronoun (it, her, me, etc.) it MUST go BETWEEN the verb and the particle. Example: I messed it up. (NOT I messed up it.) I was prepared for the questions, but I still screwed them up. (NOT ...screwed up them.)

"Ruin" means to break or damage something. For example, you might say "I dropped my phone and ruined it," "I spilled wine on my shirt and ruined it." In these cases, you damaged the items and they're no longer good. You can also use "ruin" to mean you caused something to fail, such "I didn't study and I ruined my chances of getting into a good school," or "you showed up and ruined my date!" In these cases, someone's action caused negative consequences. "Ruin" generally means that the item or situation can't be fixed. "Screw up" and "mess up" can both be used interchangeably and have a similar meaning to "ruin," but it's not quite the same. If you make a mistake you might say "I screwed up," or "I messed up my chances of getting that job." You can also use it when you damage something, such as "I messed up the paint on my car when I hit a post." However, "mess up" and "screw up" don't necessarily mean the item/situation is beyond repair.

They're interchangeable. After all, if you screw something up it doesn't really matter what it looks like any more.