Isn't it considered more traditional to put the e at the end of the sentence?
Yes, it is. Though it's not wrong, per se, to put it where it currently is. Most natives would have it at the end, though.
Only Cheannaigh sé crann nua agus chuir sé é sa ghairdín is considered right in the pick & choose part - picking Cheannaigh sé crann nua uisce chuir sé sa ghairdín é. penalizes you
But what's that 'uisce' doing in there?
Ohh wow, didn't catch that...I guess that's why it wasn't accepted >.<
They should accept it. He certainly would have watered it after he put it in the garden.