Filling under door frame after laying floor

[forsy]

Have now layed the floor and have cut under door frames rather than tile around.Have cut too high and wish to reduce the margin to say a mm.Tried putting some paper under the frame and then romoving after filling;but the filler either falls away or the paper wont come out.
Any ideas anyone-think a small margin would look so much nicer than just filling to the floor and would make it easier to paint afterwards.