@dai-bi Turn ON airplane mode before each fight. This way, if your lose, then just close out the DC game completely, turn OFF airplane mode, then reopen the game. It will be as if you hadn't battled. If you win the battle, then be sure to also turn airplane mode OFF so that it saves your win.
Also, check out what 3 dragons you'll be fighting against. If you lost the fight, either select different dragons, feed your current dragons, or change the order of your first dragon so that if the opponent hits first, it doesn't wipe out your first dragon. Then just repeat the battle. (For example: first opponent dragon has Pure and Electric elements. Make sure your first dragon does not have Legend, Water or Metal as it's first element.)
But always fight your fights in airplane mode first, just in case you lose the battle. Hope this helps.