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 heightens the urgency and panic of Sylvia's situation, showing her desperate attempts to attract the driver's attention while emphasizing the stakes of being late to school.