Does the pattern have a "schematics" section? Or does it tell you somewhere what the measurements should be for each piece of the sweater? If your measurements are on track, then all is fine. For example, if the sweater back piece should be 20 inches across and yours is 20 inches across, then all is well.
If not, then you may want to set the project down for a little while and consider your options. One option could be reading the book Knit Fix: Problem Solving for Knitters by Lisa Kartus. She has an entire section on radical fixes, including cutting and seaming a sweater that is too large.