The reason your dress made with a vintage pattern doesn't fit right is probably one of two things:
1. You neglected to add shoulder pads or do the necessary alterations to eliminate the need for them.
2. You are not wearing the proper foundation garments that women in the 50s would have worn under such dresses.
Keeping those things in mind, you should probably make a muslin (using the wonderful techniques described in Susan Khalje's Bridal Couture, which is a book everyone should own) and expect to do some altering. Also, sizing is different in vintage patterns. You may be a 10 in stores, a 14 in modern patterns, and an 18 in vintage. Deal with it and always always go by your measurements instead of what size you THINK you are. I promise it's better this way, even if you end up taking something in. It's always easier to take in than to let out. :)
