The fare class on the statement is a bit of an oddity. You should not have a problem.

It used to be that all of my UX flights posted as Y and all of my mainline flights which were not upgraded posted as K, while all of my upgraded flights posted as the class of service flown (C or F).

Then, suddenly, things switched. All of my non-upgraded flights posted as K and all of my upgraded flights posted as Y.

Lo and behold, last week, another switcheroo. My upgraded flights were showing in the class of service flown.

No rhyme or reason to it, but also no reason to worry.