Strange Eagle Copper Pour Issue
In Eagle, the actual final boundaries of the pour are constrained by things in addition to the polygon itself, including the width of the line used to define the polygon and several of the DRC clearance settings. In this case, it sounds like your pour is keeping away from the edges of your board as defined by your dimension lines. You can reduce this clearance in the DRC settings, but I wouldn't recommend reducing it to zero, as this can cause problems in fabricating the board.