Hi there,
I think you need to revise imperatives, that is verbs that order you to do something. The sentence gives you the vocative ἑταῖρε as a clue. There's a good chance that when you see a vocative noun, if there's a verb nearby, it will be an imperative.
Are you doing some work on the Aorist at the moment? Take another look at the ending on ἔβλαψα, which person is the ending?
Also, check the οἱ, did you mis-copy an oὐ? and check the breathing on the οὑδέν (it should be smooth). Remember that in Greek a double negative is still a negative.
Have another try.
:)