most sensitive test? and anyone used sainsburys own?

[bigandbeautiful]

Ok AF due today, been feeling weird so took a test this morning with fmu it was a sainsburys own in the casing. So it was a BFN until i took it out of the casing and saw a faint line. This was after around 15 minutes.
So i read the instructions and said npot to read after 30 mins?
So how long until evaporation lines occur?
Dopes it matter that i have taken the casing off?
Which test is most sensitive on the market that i should re-test with?

thanks anniemac, i know i am just trying to convince myself.
The instructions say you will see a result in 1-5 minutes and do not read after 30 minutes due to evaporation lines.
the stick was still very wet when i opened it, if that makes any difference?
Will test again tomorrow or see if i can hold out until sunday will be p**d if i spend £10+ on a test for no more answers today.
What will be will be!!!!