French Connection black long sleeved mini dress

Demure black long sleeved fitted dress with pretty lace detail around neckline. Size says 8, however this is not a US size 8 at all, not even close. I am 5’3 120 pounds and I can fit this but it is a bit tighter than I like. I typically wear a size 4 in dresses so maybe this is sized incorrectly. Fitted thick fabric with stretch. Best for size XS and small. Questions? Please ask!