i had the same test thrice. the first time baby was measuring little small, and the 2nd time, baby was not lying in proper position. and finally the 3rd time they wer able to measure it. its normal, dont worry. just before going for the test, eat properly, walk a little, just see the bright side u r able to see the baby twice.
I had the test done and the baby was in the right position. They are trying to measure your baby's nuchal fold. Were you given another date to come back to try again?
I've never heard of this test but...my daughter was always in this position so we didnt know her sex until she was born