I have this jacket (Jolt white denim in size Small) in my closet with the tags still on it. I have the red version and it fits nicely, but the white one in the same size is too big in the upper arm and bust area yet the bottom half fits well. If I size down to XS the bottom part will be too small because the small just barely buttons.
Your jacket fits you better than mine does. I don't think yours looks too big, especially if you wash it. I'm tempted to wash and dry mine but will probably return it and keep looking.