Last month dp and I had a contraceptive failure 
Anxiously waiting with baited breath for enough time to pass so I can find out for sure, no period has arrived (although may be a little early), and I'm peeing 10 times an hour (only slight exaggeration) and this morning woke up to be sick with no reasonable explanation!
I'd bought an early testing kit, did the test but it didn't work
As in no control line in the window etc, I followed all the instructions exactly and I'm no stranger to these kinds of test so I'm confident I used it correctly.
Wibu to take it back and ask for another? I know it's a bit gross but if it doesn't work can I do that? Or just take back the box but not the actual test? Or shall I just chalk it up to experience and buy another one? I know it's not really a lot of money as such but they are quite expensive and I've recently lost my job so need all the help I can get.