Your size of the gestational sac
corresponds to age correctly.
Usually fetus can be identified at an early age of 6 weeks and heart beat around 6.5 weeks.
Around 8 weeks fetus and development can be seen clearly.
This depends on many factors like quality of USG and the technician.
There is also an entity called as anembryonic gestation, where an empty ovum grows, this means there wouldnt be fetus in ovum.
It can be identified by your blood HCG
changes, since there is a difference between blood HCG value of a normal fetus and this.
Urine HCG wont help in this regard.
You need to consult your GYNC for further action immediately