If you want it to be at its most accurate, I would wait until you miss your period, and even then it can be false negative. I know how hard it is to be patient, but pregnancy tests aren't the most inexpensive thing to waist. So its your call.
Most of the time an evaporation line looks clear with no color. However it should take at least a few minutes before coming. Maybe your reading it wrong. Take a different brand of test that would probably help. Or completely eliminate the problem and just get a digital test that will read Yes...