If the tech or doctor didn't act concerned, it is doubtless normal. You (who I presume have no medical degree) really don't want to spend your whole pregnancy second-guessing the trained professionals who do your medical assessment, it is too exhausting. Try to relax and trust that you will be told of any problem or issue.
I don't really understand what you're describing? Remember at 13 weeks they are so tiny. They are barely getting legs and arms going. It can be very difficult to tell what is what on an ultrasound, so try not to stress.