You can only use a pass for a maximum of 2 days in your home country, if you have not used both of these already then yes you can use a day for travel in Netherlands.

I have used my pass for an outbound and inbound journey from and to the Netherlands so then I can't use it for another day in the Netherlands, right? 

That is correct. If you have travelled on 2 days in your country of residence, you can only use your pass outside of your country of residence. 

It is possible you have 3 in-/outbound days in your pass. If that is the case you can use it in the Netherlands for your last day.

How do I check that? 

Under ‘My Pass' after selecting your pass you can find

Outbound/Inbound

x/x used