Yes, you need a visa. Canada requires all persons traveling on refugee travel documents to obtain visas, regardless of which country issued the document.
Note: Holders of Alien’s passport and Stateless individuals need a visa to visit or transit in Canada.
(Note that "Alien's passport" means any travel document issued by a state to a non-citizen, including 1951 convention refugee travel documents, 1954 convention stateless person's travel documents, and non-convention travel documents. Your Vluchtelingenpaspoort is a 1951 convention travel document.)
I can't say how you managed to get an eTA from Canada, and even if you manage to convince the airline to allow you to board with it, CBSA officers at the port of entry in Canada will not be amused, and will likely detain and remove you, if you attempt to travel there on the eTA. It is possible to withdraw your eTA application, but no refund is issued.
In your case, I would withdraw the eTA application, and then apply for a visa. You can apply online for the visa. Note that Canada has no Visa Application Centres in the Netherlands. It will process your visa application through its Vienna, Austria, visa office, and you will have to visit a Visa Application Centre elsewhere in Europe to give your biometrics and submit documents; as far as I can tell the nearest one will be in Düsseldorf, Germany.