$50 is an abritrary initial spending limit (Shopify requires us to establish monthly billing limits). You are only charged when you sell tickets. So if you install the app, approving the $50 limit, then sell 5 tickets and uninstall the app, you would be charged $5.
Do I increase this limit myself?
Try refreshing the app, you should be automatically directed to the Plans tab where you can increase the billing limit.