Fitting bulkheads in Chesapeake Sport Tandem

Howdy!  I'm building my first boat and so far everything has been moving right along with the help of a few friends.

 I'm having trouble fitting my aft bulkhead.  The side panels seem flush but the bottom panels seem like they are sagging.

 Close upBulkhead gap

If I trim the bulkhead to lower it won't that mean it won't sit flush again the sheer clamps?  Also this is my first post so I hope the pictures worked...

 Thanks! 

Oops.  Well here's the links to the two pictures on tinypic;

 http://tinypic.com/r/afaffa/7

http://tinypic.com/r/s41ao8/7