Fork crown races are often press fit... on a new fork it is not unusual for the crownrace seat to need milling prior to installation of the bearing race. Also, there are two standards (ISO and JIS) that are not compatible. JIS crown race seats measure 27.0mm and ISO measure 26.4mm. While it is unlikely that you have fork that has a JIS spec crown the fix to install an ISO headset is the same as preping the crown race seat...having it milled to the correct spec. These tools are expensive so a visit to a good LBS which has the proper tools is probably needed.

-j