I have to take a blood test tomorrow.. not a drug test, im afraid because i smoked about 3 1/2 weeks ago.. is my system clear?

YES/NO: I assume you mean by " smoking" that you smoked marijuana, it usually can be detected up to 4 weeks after smoking, if they are testing for it, it may show in your system, though you are on the border for that. I suggest to stop smoking marijuana, as you may know it is associated with development of what is referred to as "amotivational syndrome" as well as increased risk for psychosis.