It's too darn tight...

So I bought this jacket online in a size 8 and it won't go over my shoulders! I'm normally a size 8 in tops and jackets. I think it would break it if I actually put it on. My weight is the same as ever, so I have to assume topshops sizing in this is a bit off...as it's really tiny!
It's a nice interesting jacket! I think I would probably need a 12. I might see go to the actual shop to try...