Not sure what kind of cement you use, but here is what I would do. Using Tamiya Extra Thin, I would start at the back of the tail and slowly close it up from there, working an inch or less at a time. When you start, if you hold the two fuselage halves together at the back of the tail, leaving a tiny gap between them, you tap the Tamiya Extra Thin brush on the seam to get some cement in there. Then I usually hold them in that position for about 20 seconds, giving the cement time to melt the plastic (with it being down in the tiny gap, it won't evaporate and will have time to work). Then I press the two halves together at that single point and squeeze them until a little bead of melted plastic comes out of the joint. At that point, with your project, I would clamp it on both sides of that little glue joint and give that overnight to cure. That will give you a solid base of support for slowly zipping up the rest of the joint, using the same method above. But now, you can speed up a little bit to a little section every hour or so, clamping (or taping) on both sides of the little joint until you have it all zipped up. This method will allow you to slowly bend and flex things along the way to bring all of your panel lines into alignment (hopefully) and make sure that you don't have a step between the two sides of the joint. When you're pressing the joints together, the plastic will be soft enough for you to adjust things before clamping when you're happy with the positioning. Trying to close the whole thing up all at once is going to be like trying to push a rope. Establish a base structure at the back so you don't have every part of the joint fighting against each other.
I usually don't mess around with putty when filling gaps. I prefer to use Gorilla Super Glue with the light blue cap. You don't have to worry about that cracking later on when you're working on the rest of the model, and the only parts of it that will come off will be the parts that you deliberately remove. I just give the stuff overnight to cure, then scribble along the cured bead of super glue with a black Sharpie to act as a leveling indicator, and then just wet sand with progressively finer grits until all of the black is gone. If you use a toothpick to apply just enough super glue to fill the gap, and then start with a fairly fine grit of sanding stick, you can minimize and sometimes even completely avoid damage to surrounding detail if you're careful. About 98% of the time, that will get the gap on the first try. Life's too short for the old fashioned putty, sand, repeat dance. 