One problem could be the amount of "ease" built into the pattern. Take your bust measurement over a good fitting bra. Then look on the bodice front pattern piece. It should give you the bust measurement for your size including the ease added into it. It shounds like you could have used the next smaller size. You will want to check the waist and hip measurements on the patters as well. Some patterns may have 6" of ease built into them, while others barely have 2" built in.