Here is how I would continue the story:
Suddenly, Anna felt her feet leaving the ground as she was pulled along by the string. She screamed as she started running, being tugged by the kite overhead.
Anna stumbled and tripped, dropping the string from her hands. The kite soared up into the air, dragging the string up with it.
Anna laid in the grass, catching her breath. What an adventure! But she was glad the kite was no longer pulling her along.
She watched as her kite floated high up, dancing on the breeze. For a moment, she worried it might fly away forever. But then it drifted downwards, the string unwinding from her ball of string.
Eventually, the kite landed gently a short distance from her. Anna smiled, glad she had such a fun day flying her kite. Her heart was racing from the excitement, but she felt a great sense of joy and accomplishment. It was the perfect memorable end to a perfect day.
How's that for continuing and ending the story? I tried to keep building the excitement and adventure while also resolving it happily in the end. Please let me know if you'd like any modifications to the story. I can generate additional details and plot points.