I think Amy did not want to get in trouble
I think you hit on a reason. At that point she may have been afraid she had made a mistake in going with this man, but still thought she could deal with it. Either she thought she could get out of it, or she was truly afraid by then.
Who Killed Amy?
Timeline
3:00 pm
Amy last seen by others at Bay Square Shopping Center
3:14 pm
Amy's brother called his mom at work to tell her Amy was not home. Mom thought she might have a meeting after school and told him to call back if she wasn't home
3:30 pm
Amy's brother called mom again and said she still wasn't home. Mom is a little suspicious and starts getting her things together to go home
3:40 pm
Amy calls her mom from payphone. Mom thinks she's calling from home. Brief conversation, Amy only gave one word answers. Robert Ressler says killer was right there, knew he had to make her call. More complicated, personal and well planned than most child abductions.
Approx 4:00 pm
Mom is still suspicious, packs up and goes home
4:30 pm
After arriving home, mom searches the house and gets back in her car to start looking for Amy. Sees her bike abandoned at the Middle School. Drives a few blocks to the Bay police station, reports her missing. Bay officers pick up on it and start investigating
5:14 pm
Bay PD issues first bulletin to other PD's in the area with description of Amy, telling them they think she's been abducted - Westlake, Rocky River, Fairview Park, Avon Lake. (JMO, he may have taken her to Great Northern Mall in North Olmsted, south of Bay).
6:00 pm
Amy's dad arrives home from business trip, learns Amy is missing, goes to police station. Meets with officers and FBI, begin search
7:00 pm
Massive search begins. Amy's dad goes with a large group of officers to Cahoon Creek, near the Middle School, and walks it all the way to Lake Erie, searching for Amy along the way.
It all happened very fast, but the killer had a plan. He had figured it all out.