False negatives

I have a concern on a false negative on the tests I've been taking. I have the clearblue digitala the ones that say "pregnant" "not pregnant" and on the outside of the box it says to cover the dip stick in pee for 5 seconds. Well stupid me just took the last one and only dipped it in the cup for the 5 seconds. Well after it said "not pregnant" I stupidly read the directions and it says if you're peeing in a cup and dipping it in to hold it in the pee for 20 seconds and I read online that this could give you a false negative, is that entirely true? Or do you think I'm really not pregnant if that's what the tests said.