I hate to respond with the same thing again I'll just copy and paste it : You are not meant to use your own ads before it's published, even says it on the link you shared. You can however set up your device as a test device on admob, this allows you to test your own ads in a safe way.
Hey thanks for putting up with me hahah
Yeah you're right, I had to get my app approved first in AdMob for the ads to work at all. At first I thought my app didn't need to get approved if I had the "Test mode" box checked in Construct 3. I thought by having it checked I would still get test ads to show up in my game.
Thank you everyone for the help!