The app made $300 last month and $500 this month. It indeed hasn't been very long, and I agree that $500/mo is a bit of a generous take. However I do plan on adding extra paid features which I think will push that even further.
For the SEO could you go after Gym Noobs like me who know nothing about different programs, teach them what 5/3/1 is and then lead them to your app? Or is that too crowded and difficult?