Delivery settings for slow motion

I have shot footage in 50p. Imported the footage to davinci 15 into a timeline with settings of 25fps. Yet when i try and change the frame speed using the retime curve and deliver the clip, it still chucks out the clip at full speed. I just can't find a way of doing this. The clip is playing at the speed i want in the timeline. It's just when i output it,that it reverts to the full speed! What am i doing wrong?