Du kannst nur an 2 deiner Reisetage im Wohnsitzland reisen:

https://www.interrail.eu/de/interrail-passes/interrail-mobile-pass/mobile-pass-faq/how-can-I-travel-in-my-country-of-residence-with-a-global-pass

Das heißt, die anderen 2 Reisetage kann ich nur im Ausland nutzen, ohne mein Heimatland zu betreten? 

Genau. Du kannst aber eine zusätzliche Fahrkarte für die Strecke in Deutschland dazu kaufen.

To make it clear:

For any Interrail Global Pass, irrespective of length, you can freely use up to 2 travel days of your pass in your home country for journeys to assist your travels. Your home country is as listed on your order,

On those days you can travel wholly in your home country or in any number of the member countries as long as you start all scheduled journeys between 0000 and 2359 CET.

On these (as on all travel days) you can travel on as many trains as you want including in your home country.

These 2 days are part of your pass travel days and are not extra.

Although called In/Out days they can be used without crossing borders, or both as Ins or Outs. Equally you can make other arrangements and save them for travel in the rest of Europe.

This is policed by your app and as you have seen it gives you a warning if your intended journey will take one of your 2 I/O days.