For future reference, it's sometimes cheaper to make the change after the outbound has been flown.

But of course that holds a risk that the fare you found for the change will no longer be there. If you were comfortable with what you found, you did the right thing.

As for cancelling, you can call to cancel, and you can reuse it later for a change fee. or you can Or just no-show it, but then you're throwing it away.