Okay so I took a pregnancy test the yesterday and i was at a public place so I had to make it quick…

Okay so I took a pregnancy test the yesterday and i was at a public place so I had to make it quick and discreet. I didn't wait the full time and just saw that there weren't two dark lines. Well today I took it out of my purse and there is a faint second line, do all pregnancy tests do that when there old? Or should I retest?!