How Hard Is It To Make a 16 on the ACT Test?

My best friend and I plan on taking the ACT on Saturday, and I've never taken the test before. I also haven't really studied yet, but on my English pretest I took, I made a 20 on it. I know most of you will tell me that I should have studied more, and that cramming isn't good for me, but I am going to spend all of Thursday and Friday doing pretests and reviewing and such. The college I plan on attending, provided I make the grade on the ACT, will allow conditional admission with a 2.0 GPA (I have a 3.0) and a 16 ACT. They allow unconditional admission with a 2.5 GPA (I have a 3.0) and an 18 ACT. My question here lies: How hard is it to make a 16 on the ACT? How about an 18? I'm really stressing that I won't make the grade and my future will go down the toilet, Thanks!