Yes, the accent is different and in fact they are two different words. περνάω means to pass while παίρνω means to take.
More commonly the two latter ones, but in formal situations it can used as the first option as well.
I'm still lost. What's wrong with "I take it". Is it just the spelling although the pron is the same?
The difference between "παίρνω" and "περνώ" not a mere difference of spelling but that they are two different words.
What kind of exercise was this? I'm assuming it was listening and from what I see your answer was correct. Please tell us what kind of exercise this was so we can try to understand why your answer was not accepted.