Flat onion looking skin in loose stool (only 1)?? worried i have tapeworms??

Unlikely: If you live in the USA and have not traveled, then tapeworms would be very unusual. The likelihood is that this is just something you ate which was only partially digested. If it does not recur and you have no other symptoms would ignore it. If it recurs, salvage it and take to your doctor to be examined professionally. Good luck and best wishes.