You've likely taken a bike which wasn't locked by the previous user. Then your card is not coupled to the bike resulting in you being unable to unlock it. But probably a rental period will never have started on your card, so it shouldn't cost you anything.
When using OV fiets, it is advisable to activate OV-fiets ritinformatie in the NS app, as this will give you a push notification when a rental is started or correctly ended.
For now keep an eye on your transactions, emails and invoices. Should you get an email that an OV-fiets is in use for more than three days, then contact customer service immediately (by phone or social media) to have the rental stopped manually.
@Daniel you were right, prev user didn't complete the ride properly, so it was unlocked when I took it.
I contacted NS customer service few times, they confirmed ovfiets was not linked to my card. They will send NS colleagues to pickup the cycle where I have parked it.