Without knowing more about your strokes, it is hard to really say, except for one thing.......
As a rule of thumb, a dive 50 fly on the front is about the same for a push 50 free on the end.... for an IMer.
So, either you went out too hard or you really died on the end. Keep trying to get the first and last 50 closer on future swims.... say 40 going out and 40 coming back. Your middle 50s will come down, too, by going out a bit easier. Just don't drop the legs too much on the fly and you will be good.
Without knowing more about your strokes, it is hard to really say, except for one thing.......
As a rule of thumb, a dive 50 fly on the front is about the same for a push 50 free on the end.... for an IMer.
So, either you went out too hard or you really died on the end. Keep trying to get the first and last 50 closer on future swims.... say 40 going out and 40 coming back. Your middle 50s will come down, too, by going out a bit easier. Just don't drop the legs too much on the fly and you will be good.