Not sure, I think it can go either way. Those PG tests are quite accurate - mine showed up positive after 30 secs! The only way to be sure is to wait a bit longer, which must be agonising. Hang in there and hope you get the result you want tomorrow.
This happened to me twice before getting pregnant with DC2 and I was ttcing and AF always 28 days, could be that the egg didn't implant I think thats what happened to me. I even got morning sickness, but I always get it very early on before I can test. Pregnancy tests very accurate I'm afraid. Good luck.