Well, blood tests are generally accurate sooner than urine tests, and at the very earliest
, a blood test will be accurate about 6 days before your expected period. Urine tests take longer. Some women do get positive urine tests 4 days before their expected period, but most won't until 2-0 days before and even some don't get a positive until after they've missed a period. So yes, at a week before your period is due, a urine test would not detect a pregnancy.
To get complicated, this is how they work: Pregnancy tests work to detect the HcG hormone which may be present (in VERY small amounts) in a non pregnant women but rises quickly once a fertilized egg implants into the uterine wall. Implantation occurs anywhere from 6-12 days past ovulation. The amount of HcG will generally double every 48-72 hours, and a test will not become positive until the amount reaches at least the test's sensitivity level.
She probably only had you do a urine test because you could see the results right away, plus just in case you ovulated earlier than you thought and would therefore be further along in the pregnancy.
I would wait to see if you get your period before testing again...but tender boobs is one of the first pregnancy symptoms noticed
Sorry to be so thorough and good luck!