I think you may find the big game is on Saturday 11th May, Selby's outstanding postponed games against Moortown comes first and they will play Medicals midweek
The RFU website shows you are correct ,the below fixtures are shown as remaining
Saturday, 13 April 2013
Bradford Salem Vs. Selby
Castleford Vs. Sheffield Medicals
Doncaster Phoenix Vs. Skipton
Hullensians Vs. Roundhegians
Leodiensian Vs. Ripon
West Park Leeds Vs. Moortown
Yarnbury Vs. West Leeds
Tuesday, 16 April 2013
Selby Vs. Moortown
Wednesday, 17 April 2013
Yarnbury Vs. Sheffield Medicals
Saturday, 20 April 2013
Ripon Vs. Moortown
Roundhegians Vs. Leodiensian
Selby Vs. Hullensians
Sheffield Medicals Vs. Bradford Salem
Skipton Vs. Castleford
West Leeds Vs. Doncaster Phoenix
West Park Leeds Vs. Yarnbury
Saturday, 27 April 2013
Selby Vs. Sheffield Medicals
Saturday, 11 May 2013
Doncaster Phoenix Vs. Selby
Hope this helps with some confusion in this subject, taking it that the RFU website should be correct.