English to Latin Translation: "Save nothing for the swim back"

I'm looking to use a line from the movie Gattaca as a latin motto: "Save nothing for the swim back". The context is about two characters who swim out into the ocean to see who can swim the furthest. When asked how the weaker swimmer wins, he says he did it by saving none of his effort for the return swim to shore.

I take it to be a great way of saying to never to quit and to focus on your goals rather than on the risks. I tried translating it myself and got: "Reservare nihil in natare retro." Is this just a literal translation though? I want to make sure it makes sense the in the context I described above.

Thanks!