THE OVERALL PICTURE
If you are serious about shopping, you should take armfuls of clothes into the changing room at any one time, and try pieces on that together make up an outfit. It's much easier to get an overall impression of a new wrap-around top if the bottom half looks right.
WHEN SIZE MATTERS
Every retailer will size their clothes for a slightly different fit, and there is no such thing as a standard dress size. Don't only try on one size; take the size above and below what you think you are, and see how they fit. Sizing can be inconsistent, so judge by how the garment feels and falls on your body, not by the label.