Since you're quite skinny and not a big smoker, a little less than a week?
I mean, I don't have a scientific answer, don't quote me on that, it's a guesstimate.
So yeah, if the test is 4 days after you last smoke, I'd guess you might still have some in your system. If you can put a bit more daylight than that between the smoking and the test, it may well be clean I reckon.