Why did I wake up and say ouch during my first colonoscopy?

Light sedation. You are only given the smallest amount of sedation necessary. You were aware of the sensation, but this was not a problem.
Sedation. Some colonoscopies are done using versed and demerol, (meperidine hydrochloride) others use valium, others use propofol. Yours may have done using conscious sedation with not enough Demerol (meperidine hydrochloride) to reduce the pain.