Possibly. Miscarriages are common and can appear as a late period.
Go back for the test on the 10th. There are two types of pregnancy tests. The first is a "qualitative test." It only determines IF hCG is present, this is the common home type of urine test. The second, a "quantitative test" can tell the actual amount of hCG using a sample of blood.
HCG rises rapidly during pregnancy. The numbers should go up, significantly.
5 mm is very small, you may not even notice if the sack was expelled in any blood. A pencil is about 6mm in diameter.