6 weeks ultra sound and all they saw was a sac with two rings

I went in today to a pregnancy clinic to get an ultrasound and they did a vaginal U/S I am 6 weeks and all they saw was a sac with two rings nothing else no yoke sac, nor a fetal heartbeat nothing.  Is it to early to see anything?  I called my doctor today and they told me to go to Lab core and get blood drawn and I have an appointment with my OBGY tomorrow.  Should I be worried.  The lady at the clinic told me that I am going to have a miscarriage.  This is my first child so I am really worried.  If anyone has any advice please let me know.