The paragraph that would help build tension if added to the story is:
"As she struggled to free herself, the bus pulled into view. She waved her arms wildly, but the driver didn’t notice her. And she was still stuck. What was she going to do? She could not be late to school today."
This addition enhances the tension by illustrating Sylvia's frantic struggle and the urgency of the situation as the bus arrives without her being able to free herself in time.