Advice please

Ok, I'm going crazy(it was a short trip). Took a target brand test this morning with FMU and got a BFN. It is a blue dye test. I should have AF no later than tomorrow if my calculations are right. 
​So I've got the nagging feeling I should retest. My gut is nagging me so bad, I went and looked up the sensitivity of that test and it is the lowest they make at 50 unit of measure escapes me at the moment. 
​Ideas? Advice? Trying to not stress but I can't get over this nagging feeling.