In the current scenario, I would suggest a trans-vaginal sonogram to clarify the situation. Doubling serum beta-hCG titres are suggestive of good progress of pregnancy
even though the individual values may be lower than normal. In addition, if you are at least one week past your missed period, the sonogram can pick up a gestational sac
and also the viability through fetal cardiac activity and fetal pole
. If investigations indicate an unfavorable outcome, then it is a miscarriage
. So, please wait for some more time before things clarify. Wish you good luck.