I thought the same.  The small scrap piece was my original "test" cut and it now fits just fine.  I guess my cut is ok, I even cut a little more out of the actual board that I will put in.  I believe the floors were not line up even on either side of the jamb.  I'll try again today to get that piece in.  When scooting the test piece in, I have my wife and son stand on the floor on either side so it would not move.  Good idea?
What I am worried about now is the ~1/4" or 3/16" difference in the floor spacing against the baseboards on the one side now that the test boards fits both sides. It does not appear that I have much wiggle room on the other side to get them about the same.  I snapped chalk lines to see if these outside walls were square and the seemed to be.
here is a pic of the jamb area

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