No problem. The parts I would have marked in my students' work are all at the end of your story:
Not that I hadn't begun (Tense is OK, it's just the participle)
Glaring at me is the upturned hem ... (It's the walk in the park)
I didn't know what to say to this... He laughed again ... He didn'twait (Flashback)
... mind returns back to the present ... it strikes me ... like there is a relief (better still:
as if there were a relief - but that point is certainly disputable if you want to write informal language)
... has built up ... has become me (Walk in the park)
Perhaps your teacher didn't have the time to read your story very carefully - or she's less strict in matters of tense.
