evap line? explain evap lines to me please

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* I also posted this in "am I pregnant" didn't know which board would get me more answers.**
I know these questions get asked frequently but it's never happened to me before. I'm not trying to get pregnant. I don't feel that it is very likely that I am pregnant I just got off BC because I just couldn't seem to keep up with it. I expected it to mess up my cycle and originally I thought I was late because of a miscalculation due to having 2 periods in may. (Yay BC!) so I took a test and I stared at it until my pee faded away. Negative. I was relieved because I'm not wanting a child yet, not until after my vacations are over. I don't wanna be pregnant on a cruise ship and I have 2 cruises one in the summer and one in November. Anyways so hours later I walk back in to the bathroom and see this positive ass looking test and early had a heart attack. My period isn't due until around the 2nd so really, I'm good. I took another test remembering this is most definitely invalid and it's negative. 
So...
Y'all I should be able to stop worrying now right?? I've never had an evap or a false positive ever. I always thought Evaps didn't have color. 
I didn't bother posting a pic of the negative cause it's clearly negative. Ignore my gross ass cup holder.