You've done everything you possibly could and in all honesty, more. It sounds as though you take phenomenal care of your animals and chances are, it's your best bet.

It's a sad loss but you've still got another frog to strive to keep happy. Everyone makes a mistake at one point and at least you were willing to step up to the plate and attempt to make the frog as comfortable as possible.

You should, personally, be happy that you've done everything in your power to make the animal as happy and as healthy as possible. And although this story doesn't have the fairytale ending, you've been nothing less than a knight in shining armor to your frog. <3