I don't think u should worry, I read about the sleeping positiions too, and I think its just a guideline, i've been trying to sleep on my left side (i'm 13 3), and I manage it most nights, but lately i've been finding it more comfortable to sleep on my back, which they say isn't good. I think it shouldn't make a difference.
My sister in law with her first baby, had such a smooth pregnancy that she managed to sleep on her stomach (or as close to be sleeping her stomach as was possible) even on the night before giving birth!!!, and her baby was absolutely fine!!
Hope this helps
xxxx