1. "Your professors are going to be a lot harder on you in college!"
While there are some professors who are fairly strict, I've personally found that my professors are no more strict in college than in high school. There are many of them that are so much more lenient in college. I've had a professor straight up say, "I don't care if you're eating. I don't care if you're on your phone. I don't care if you're in your pajamas. I don't care if you don't show up to lecture, just be there for the exams." Pretty much, they don't care about much. Most of them just want you to either be present for the lecture to get your attendance points, or they want you to show up to the exams. You can pretty much wear anything and they don't care. No one gives you detention or anything if you're on your phone or you're eating in class. They don't care. You pay to take their class, they don't care if you fail if you're not making an effort for the most part.
2. "You're going to have an exam every week!"
For most of my classes we have an occasional quiz here and there, but they're fairly unofficial. There's usually three midterms exams per semester plus the final. It's definitely not every week, and it's significantly less often than exams in high school.
3. "You'll have to pull an all nighter every night!"
I have a fairly difficult major - biology. It's a heavy course load. I very rarely have to pull all nighters. Unless you manage your time REALLY badly, you can get plenty of sleep at night.
This one is more from students rather than teachers but:
4. "You have to drink alcohol to have fun, that's how you have fun in college!"
While alcohol is good and dandy fun, sometimes the most fun you can have is being alone with some close friends and have a good time. Go on an adventure. Go places. Do interesting things. You can do all kinds of things without alcohol and they are just as if not more fun.
5. "Do as many activities as possible!"
I don't know about you, but I like having down time. If you do everything possible you're going to have no free time. Do a few things at a time, try something new each semester, but give yourself time to do schoolwork and free time.
6. "You and your roommates are going to be BFFs!"
While for some people, such as myself, that's the case, many people really do not get along with their roommate. It's hard to live with someone else, especially if you didn't know the person beforehand.
My personal favorite that I've heard from students:
7. "I'm not going to 'insert instate school here', it's too close!"
I don't know about you, but in my northern Delaware High School, everyone swore they weren't going to go to University of Delaware, but in the end, somewhere around 75% of my graduating class ended up at UD.