Use a baby bath thermometer while preparing the enema, and the water at prep time should be no warmer than 102-103 degrees F.
I suggest that you don't hang the bag more than 18 inches above your hips while lying down. Go slow, clamp off the flow for a minute or so if you feel a cramp until it passes and then resume.
As the previous poster stated, a gentle cleansing enema by itself won't on it's own stimulate labor to begin.