First trimester bleeding at 11 weeks(or 7 weeks?) help!!?

Im asking this question for my girlfriend. We had already went to her first appointment and had made another on may 14th for the ultrasound, we were told that she was 11 weeks now since her last period was on valentines day... but after going to the ER today they say from the size of the sack that we are only 7 weeks. She had been bleeding yesterday on and off and it happened again thismorning so we went to the ER to get checked out, they ended up doing the sonogram to see the sack, and then measured it, since we couldnt see anything but a black circle. From that measurement, she said we were only 7 weeks.The doctor then said that we need to go in for blood tests in 48 hours to see if the hormone level increased to see if she still has the baby and its just too early. Basically they said we are either too early or there was a miscarriage... we are very scared and dont know how to feel about the situation. Does this sound possible to only be 7 weeks now? She has a baby belly...help?