Where did you create a trip? If that's on the Interrail website, then you should know that there's no synchronisation between the website and the app, except for the start date of the pass validity period. But it's not recommended to activate a pass or any travel days in advance, other than to test/play around. In that case, choose a start date well in the future and cancel the pass activation after you're done testing. Then only activate on the day you start your trip.
In the Rail Planner app, each pass needs its own trip. Nothing you do in the app will change the trip you created on the website, so you don't loose anything. The app's main function is to manage the pass; in the connected trip, you eventually add trains you'll use with the pass. You don't have to add them now: the only requirement is that you do that before you board the train. It's the digital replacement of the paper pass travel diary.
I generally don't use the Interrail website at all to plan or to make reservations. Instead, I use www.bahn.de (more reliable) to make plans and book reservations elsewhere (cheaper and more reliable).
This general introduction is recommended:
https://www.seat61.com/how-to-use-an-interrail-pass.htm
