Fetal Doppler: Can't Find the Heartbeat Again

I have a fetal doppler and was able to find the heartbeat around 10 weeks, but can't find it now at 11 weeks.

I'm nervous we've lost the baby, but hopeful that I'm just doing something wrong or being impatient.

Any suggestions or advice?

UPDATE:

Found it! The baby was really low! When I did this with my son, I usually put the probe to my right and near my ovary. This baby, however, was hiding low and to the left!

Thank you for all your kind words and advice!