Well, I did some internet (very scientific

) research on your behalf. It seems that the blood test you had yesterday that said negative is qualitative and just measures yes or no. It is not that sensitive, so if the HCG is there but is under 25 it may not show up as "yes". The one they sent off is quantitative and will measure the amounts to the smallest degree...so if it is there it will say so. Some urine tests are actually more sensitive than the qual. blood test.
However, on the negative side, apparently HCG clears out of blood faster than it does urine, so if it's just a chemical pregnancy it may have already cleared the blood and is still lingering in the urine....