how do I know if it's an Evap line?!

Ka
Took hpt and then had to call my daughters doctor. I came back to check the test, an obvious negative. So i fixed my daughter lunch and went back to the bathroom and it's definitely a faint positive now (less than 20 minutes) but the test says do not read after 10 minutes... 
I really don't want to take my sick child out to the store right now 😩