Ans OP question in comment.
Updated to change the glue to be used.
1. to help with the glue mess, place transparent packaging tape along both edges. Tape as close to the edge as possible.
2. You may have to insert a couple of thin wedges, screwdriver, etc. in the gap to get enough clearance to get the glue in
3. use a glue wedge tip or screwdriver to ...
being furloughed I have time to attack my 1978 year old bathroom, ripped out the original shower one piece install. Had a professional install a heavy duty fiberglass shower pan with center drain.
Originally we were going to install a Schluter shower system(way to expensive)so opted to go with the cement board install.Shower pan is exactly a 48"W x 36"L and ...