Actually, a speculum doesn't touch the endometrium. The endometrial lining is the inside lining of the uterus. The speculum is an instrument designed to look at the cervix and the upper portions of the vagina.
It may contact the outside of the cervix and irritate it a bit, which may cause some spotting.
As was mentioned, if it is just spotting and stops shortly, it was probably related to the speculum exam. If it continues, call your doctor back for advice.