Navy and White polka dot Kimono Style Dress

NWT Blue and White Kimono style dress. I ordered the dress online and the tag shows it as a UK 10 but it fits more like a UK 6(US 2/4). I typically wear a US 4 (sometimes a 6) and I can get the dress on but it will not zip. Feel free to ask any questions and I will try my best to get the accurate sizing on the dress!!