I had complete previa also. was diagnosed at 20 weeks scan. started spotting at 30 weeks. scan at 31 weeks confirmed it hadn't moved. had 2 big bleeds and delivered at 34 weeks. mine was running anterior to posterior. my ob cut through my placenta when I had my c/s. there are chances of it moving. mine unfortunately didn't. there is a group on fb for those with previa who are seeking advice and support from others in the same situation or have been in the same situation if you are interested. let me know and I can pm you the link

good luck and I hope it moves for you!