Two things... first, my wife has broader shoulders than I did and nobody ever doubts that she's female. Secondly, it's not just about the width of your shoulders in isolation (and I lost a LOT despite being a weakling with no shoulder muscles to speak of, btw), it's about the ratio of shoulders to hips - every inch HRT adds to your hips will make your shoulders seem at least 2" smaller. 🙂 Cis women with a "socially desirable" build generally have shoulders about the width of their hips or a little smaller, so looking like that will be sufficient to make anyone assume you were born female, especially at your height.