When I say open your app above, I don't mean while you're trying to fly. Your bird should be off.
Your nexus 7 can't receive two wifi signals at once. The bird should be off and you should connect with an internet signal - that is, a router that's broadcasting internet via wifi.
So your app should then connect to wifi with internet. Look at your device's settings and make sure it is telling you that you are connected to the internet. If it's not connected to a wifi internet signal, force it to connect. Once it's connected, open the flight app WITH THE BIRD OFF and get your maps cached.