Good morning ladies,
BAngie, sorry that your app didn't go as plan. big hug to you

if baby was moving around alot and the heartbeat strong, i dont thing there is much to worry about.
remember they work on averages and he could have just stated that baby is small - that is not a cause for concern, as very little babies are actually on the average.
if he is small, he will just monitor some things more closely, like blood flow to the baby, etc. when they are big the monitor other things more closely
and yes, if baby is smaller, it might take more time to properly do the downs screening (my gynie only do the downs screening at 20 weeks as she say baby is just to small before that. she send her patients for the fetal assessment if you really want to do the screening at 12 weeks)
and if baby is lying so low, even the next scan might be tricky if baby moves around alot.
and yes, he would have definately told you if he though that there is something wrong
i really hope and pray with you that all is well with your baby