I read up a little bit about what I needed to do to get the 'good' endings, and it looks like you don't need to be 100% Paragon or Renegade to get the right options at the end. But you did need to use the Charm or Intimidate options each time you
(SPOILER)talk to the Illusive Man, which I don't think I've done. Oh well. Can always go for that next time, when I get the ME trilogy.
I also read that to get those readiness scores up above 50% you have to play multiplayer, and that those scores determine how good an ending you get. That sucks because I had no interest in the multiplayer part of this game and I'm probably pretty bad at it.