Pregnancy test - Very dark negative?

Hi! I just took a home pregnancy test which came out negative. It's one from Boots with a control window and another where the result comes up. A cross in the results window means positive and a single line means negative.

I only have a single line but it is quite thick and extremely dark, much darker than the control window. I have looked through the leaflet that it came with, and tried to google, but all anyone seems to talk about are faint or dark positives, not negatives. Also, just to clarify- there is not even a hint of a second line. I was just wondering whether this is normal (first time tester) or whether it means there is something wrong with this one and I should go out and get another to make sure this first one was accurate. One of the reasons I am unsure is that the control window and the results window appear to be the wrong way round on my test (according to the pictures on the package and leaflet).