θα γυρισω αυριο ?
could επιστρέψω work here?
Not by itself.
I don't think the aorist subjunctive is ever used by itself (except in command forms) but only ever with some particle, most often να or θα.
Θα επιστρέψω αύριο should work for "I will return tomorrow" - future tense.
αύριο γυρίζω - why is this wrong??
I wrote Επιστρέφω αύριο - and it was marked red (???)