I'm confused about your question... :oops:
90 cm = 35.4 inch
I wouldn't put too much stock in the "XS" label or "S" label ... or any of the others. According to some patterns I've read, I'm an "extra large"; but on others I'm a "medium". Those "small, "medium", "large" labels are so ambiguous and subjective at best! :evil: Forget the verbage and just go by the numbered measurements. Since your bust is 90cm (35.4inch), make the cardi as specified for the "XS" size, whether or not you consider yourself an "extra small".
If you don't like the density that your correct guage it giving you, then you might want to try using a yarn of a lighter weight, maybe sport weight??
I hope that helps a little :?