for the usage it is important that the approximately the size of the VuMark corresponds to the size of the printed VuMark picture.
But i do not believe that this is the problem in your case.The following references to Vuforia Engine articles could be helpful:
1.) e.g. when you generated you VuMark database you need to set the id for it - article:
How To Work with VuMark Databases . So in the sample picture below we can see the difference with 2 different VuMark instances of the MortonTuxedos VuMark e.g. with ID0001 and 0002
You can generate the picture of the VuMark instance when you click on the link Generate Picture:
If this setting is not correct - then it could be a reason that it will not display the content . Another point could be the setting of the VuMark handler. Here I want to refer to the article :
Working with VuMarks in Unity - see the point "Scene Elements and their Configuration"
I think it will be helpful when you check the implementation of the HoloLens Vuforia Examples /from the Unity assets store. You can open the scene 3-VuMarks in the Assets/SampleResources/Scenes folder and check the implementation there - so how the different contents are displayed depending on which VuMark instance was scanned.
Alternatively you can load your database and replace the sample VuMark database by your own database. You need to adapt your VuMark handler script depending on the used ID in your VuMark database.
Vuforia Engine Support