If it's about the feeling, there's not a lot you can do. Sometimes I'm ahead and yet I still feel overwhelmed. Best way to deal with it is probably just do whatever makes you feel comfortable and take frequent breaks.
With actually falling behind and preventing it, probably try and set scheduled study times for certain things. ie. if you have weekly homework/quizzes, set aside time around your timetable to work on these things. Even for things that might not necessarily be locked in like assignments you might want to set aside time weekly to work on them. One of the many things that's harder about uni is the lack of a rigid timetable - it's so much easier to be in school and be told precisely what to do, when to do it and where you have to do it. Making your timetable slightly more rigid may help with that (but be wary of making it too much so that you feel a bit suffocated).