Im on chapter 12 right now and have done some of the missions  but I want to do them all so I need to know,  
At the end of the game is there a way to get back to Puse or do I need to go back to an earlier save ?

Ok thank you ill keep going then 

Once you beat the game you'll get a chance to save after the credits.  Boot that save up and you can warp back to Gran Pulse and finish everything up.  You wouldn't want to try and 100% the mark missions until after you finish the main story because the last Crystarium level isn't unlocked until you beat the final boss. 
 
I like the way they handle this.  You actually gain something by beating the boss other than the ending to the story.  It maintains continuity in the story where in past Final Fantasy's there was always a huge build-up in story and then this weird lull while you put the boss on hold and grind, race chocobos and whatnot.  And you don't feel like you're back-tracking to previous saves quite as much because there's progression in completing the story.   
 
Wish they would have added a 'New Game +' option though.  Getting all the ultimate weapons is such a grind and there isn't a whole lot to do with them by the time you get all of them.  Taking them through another play-through would have been nice.

" Once you beat the game you'll get a chance to save after the credits.  Boot that save up and you can warp back to Gran Pulse and finish everything up.  You wouldn't want to try and 100% the mark missions until after you finish the main story because the last Crystarium level isn't unlocked until you beat the final boss.  I like the way they handle this.  You actually gain something by beating the boss other than the ending to the story.  It maintains continuity in the story where in past Final Fantasy's there was always a huge build-up in story and then this weird lull while you put the boss on hold and grind, race chocobos and whatnot.  And you don't feel like you're back-tracking to previous saves quite as much because there's progression in completing the story.    Wish they would have added a 'New Game +' option though.  Getting all the ultimate weapons is such a grind and there isn't a whole lot to do with them by the time you get all of them.  Taking them through another play-through would have been nice. "

I was thinking more along the lines of current-gen 'New Game +" type modes where the difficulty is scaled.  Playing through a harder play-through where the focus is more on using different strategies and gear combinations than upgrading and leveling.