Not much info to go on here!
How long is the movie and what do you want to do with it?
Welcome to the forum.
Along with Craig's request for the Duration of the Timeline, what are the Export settings that you have chosen?
What is the target file size, that you wish to achieve?
Usually, when someone complains of an output movie being too big, I find that the movie was created using a lossless codec (or with no compression at all). I wrote an FAQ entry in the After Effects forum about this; it's relevant enough here that I may as well link to it, since the gist is the same: