Mariah: (my) step one done!

I finished the back piece tonight. I started with it, rather than the sleeves, because that'll be the fun part... And I wanted to save it for later, lol. I'm about to cast on for the front pieces, which, like the sleeves, I will do at the same time. The way it's looking right now, I'll have it done A LOT faster than I thought I would! I think this one might be a little too big... But I hope its just a little bit, bc if it is, I think I will steek the sides in before I seam to get some extra width out of there... I think its going to be too loose at the waist (almost for certain), and a little looser than desired at the hips because of the way it needs to stretch so the cables are visible. I have a cabled zip up hoodie that I love that I got long before I learned to knit, and I want Mariah to fit that way. But the chest is a little tighter than id like, and I wish I it was about 3 inches longer. I measured it last night, and when I compared the measurements of it to those of Mariah, I found that its several sizes smaller than what I have on the needles... BUT mine is ribbed all the way up ... It measures smaller than it fits. Its 18" lying flat, but stretches about 2 inches when its on.
Man. I wish id thought to measure my sweater before I started. :( I have a feeling I might be screwing up. I hope if I am, I can save it and make some curves all at the same time with steeking. Because I need the bust to be larger than the hips... Which is why I went with the size I did. Damn it. This is confusing, I hope not many ppl read this one, for all who do, I'm sorry for such a rambling post!