Measurements?

missability

I'm sorry if I didn't post this in the right place

So I know this may be a bit premature.....since I have only been on my plan for 2 weeks, but....I got this great jacket for Christmas that is a size 2X, I have 1 more week to return it....The only sizes available are: Small, Medium, and 3XL, (the others are sold out)
My goal weight is 145 LBS, and I am 5'6"....The 2XL I currently have fits me and I am 269.LBS...Ive lost 10 LBS so far.......Next winter this size 2X will be huge on me......So I don't want to keep it, because I AM GOING TO DO THIS!!! The only option is the size Medium.....which has a chest measurement of 40"...SOOOOO here is my question, are there any women out there in MFP land who are 5'6" and around 145 LBs, that could tell me if I would fit in a 40 inch chest jacket when I hit my goal weight?
I really really love this jacket, but if I buy a medium now, when I reach my goal if it doesn't fit I wont be able to return it, and it is expensive. I had my eye on this jacket for almost 6 months, so it was bought for me as a gift, the person who bought it had no idea I was working on a diet plan starting 2013.....so what are the average measurements for a woman who is 5'6" and weighs between 140 and 150? It has been so long since I weighed that, I cannot remember......Oh yeah, I am very average in the chest department, when I was under 200 Lbs I was always a C cup...not too busty, but not flat chested either...