Positive test after an hour?

I took this test and at first it read negative but I was very tired so I took a nap and woke up and it was positive. My period is not due until the 20th. Could it be that my pregnancy level was too low to detect rite away or is this a false alarm. I have taken several tests months prior and no matter how long the results remained the same. Has this happened to anybody else? I don’t want to get my hopes up for nothing and I’m already so excited along with my DH. Please help clear my mind!!