could have used better description or a photo...
but I'll take a stab at helping. Maybe it will spur some others to chime in.
On your question of "How do we tighten the sail?", I assume you mean that you have it unfurled all the way out of the mast. If that is the case, you need to use the outhaul line to pull the back end of the sail out to the back end of the boom. You should be able to get the sail almost flat by doing that. If it is all the way out and you cannot get it flat with the outhaul, maybe it is not the correct sail for the boat (too big).
As to your statement "the blue line is at the max on spindle", the blue line on my boat is a continuous loop, so I have a different setup than yours. The blue line is used to furl the mainsail, not pull it out. You pull it out with the outhaul line. My jib furler has a single furling line, and sometimes when setting up the boat for the season you need to either unwrap a few turns or wrap a few more turns to get the line in the correct length to fully furl the sail back up when you pull on the furling line to roll the sail back in. Perhaps you neeed to see if that would help.