What is your biggest concern in the risk?
The way I see it for me there are four outcomes: 1) Company discovers and I am fired. 2) Company discovers and has no interest. 3) No one finds out and I have decent side income. 4) The app has good success and I quit one day with a phony excuse before they become aware of it.
In my case, 1/4 is actually bad but the likelihood of discovery is low because my company is not in that field. I'm not likely to be fired without warning and it's not likely to be discovered while the app is transitioning from side income to success (before I can leave, if the app is worthwhile to litigate over).