The best (and really only) advice I can offer is to try to redirect your need to be a perfectionist in directions that will help rather than defeat your goals. If you know that you get caught up worrying about every little detail in one assignment so that you run out of time to get to the next one, try to redirect yourself to the next assignment with the conscious effort that you need to do well in ALL your classes, not just one, and if you have enough time, you can go back to the details of the first one.
You can also try following a schedule. I try to recommend students create schedules with built-in flexibility to deal with the unexpected, but for someone who is having problems with perfectionism interfering with their studies and/or social life, a more rigid schedule may be more effective. Sit down with a weekly calendar, block off the time you're in classes, the time you need to commute to and from your classes, an hour for each meal, block off normal sleep hours, and then look at the time you have remaining. Find the equivalent of a half hour per day for relaxing or doing something fun...you don't have to do it every day, but, for example, could say that on Fridays you want to go with friends to see a movie, and that will take 2 1/2 hours, so the other days of the week, you'll only take that hour for meals. Or, you can decide you really only take a half hour to eat lunch, but then become very unproductive in the middle of the afternoon, so will split that time so you have a half hour later in the day for a break or nap or to get a snack, etc.
Now you can split up the rest of the time for studying each subject. What works best for you, to focus on one subject for a long block of time, or to switch back and forth between subjects? If you need to set an alarm clock to remind you to switch to another subject, or another problem, do so. If you're prone to getting bogged down on one problem and not even getting to all the others on your assignments, then use a timer and when it goes off, move to the next problem. Do a little work on each, then go back to the ones you couldn't complete and spend time reviewing that material to make sure you understand it before attempting the problem again.
So, that's all I can really suggest is to refocus your need for perfectionism onto perfect time management.
If you really feel like it has gotten to the point where it's affecting your studies or your ability to have normal social interactions, seek out a psychologist or psychiatrist. They may either be able to give you much better strategies than those of us here for modifying your own behavior to achieve your goals, or there may be some other underlying problem that can be treated or at least alleviated with medication.
