Have you tried this sequence:
Kernel -> Restart and Clear Output
Save
Submit
The point is that the grader does not need to see your output and sometimes the output can contain syntax that confuses the grader.
If that doesn’t help, then the next key question is the one that Deepti asked: make sure you have not modified any parts of the template code other than in the “YOUR CODE HERE” sections. If you have done that, then please start with a fresh copy of the notebook as described on this thread.