How accurate is a transabdominal ultrasound in assessing an ovarian cyst? Had to stop transvagingal ultrasound, extremely painful

Depends. This depends on a number of factors: the quality of the ultrasound machine; how much your urinary bladder was distended; and particular location of the ovaries in your pelvis.
Depends. If the bladder is well distended so as to provide a "window" to see the ovary, the transabdominal ultrasound may be sufficient.