Please answer!

I took a pregnancy test this morning and nothing showed up at 3 minutes. I didn't look again until 10 and I saw something very faint. I took pictures of it but I'm not sure if it was an Evap line. It was right at 10 minutes. I went to look at it about 30 minutes after that to check and see if it was an indent and there was nothing! Do Evap lines disappear like that?