I think it's technically okay to go through the term with a conflict. But if you come across any problems, you'll be out of luck.
For example, if you have a test in the lab AND the lecture on the same day, the prof isn't required to reschedule it for you. It's the risk you take when you overlap your courses. (I think, but I'm not 100% sure)
I would suggest going to the department and talking to the administrative assistant. Chances are, there are some "hidden" spots open in another lecture section and they will be able to fix it for you.