4km out and back

Today did a 4km out and back. This is where you run 4km really easy then turn around and run 4km back hard. The easy 4k came in at 21:01 no worries there. Turned around and upped the pace, but the first km was slow in 3:57 then pushed harder with the next 2 in 3:30. On the last pushed hard and did 3:15 which was good. Time was 14:12 which I felt was slow and I think it was because the slow first km. Next time try and push harder from the start, but it still wasn't a bad run.