A jacket that doesn't fit is period accurate. Issue clothing came in 3 sizes and you got the first jacket on the pile that would button. It could fit you like a tent or you could look like an overstuffed sausage, if it buttoned it fit.
Also these were made to fit an average soldier. On average they stood between about 5'4" and 5'8" I believe. If you were much beyond those margins in either direction your jacket was going to be the wrong length no matter what. Even if it fit well in the chest.