It may have been a chemical miscarriage
:( you probably just happened to test at home at the perfect time. Make an appointment to see your own Dr to discuss it and have your blood tests redone as there is always a very slim chance of a lab mix up and better safe than sorry.
Best of luck
Your pregnancy test can't detect something that's not there it can miss it but not dectect a hormone that doesn't exist. Call your ob and make an appointment for when your be 5-6 weeks see what they say.
While it's possible it was implantation bleeding, if the blood test at the hospital came back negative, I'd say the odds are you are not pregnant. I'm sorry. (I hope I'm wrong.)