Did it come up within the time limit?
Those blue dye tests I've heard so many horror stories about them. Have you got a pink dye test you can use? How many days DPO are you? I used clear blue line tests at 10DPO and got a very faint blue line then again at 11DPO and got an even fainter line.
Got hubby to get some FRER and got a definite BFP. Did the last CB test a few days later and got a bit a darker blue line.
But it was the FRERs that convinced me.
Did a CB digital at 14DPO and got a pregnant 1-2 and then 2 days later did another and got pregnant 2-3
When is AF due.
If that line came up within the time limit i wud say that's a positive. Maybe give it a few days and test again but I highly recommend pink dye tests over the blue dye ones.
Good luck. Please keep us posted. Fingers crossed