Loose cranks ultegra 6800

Noticed a gap between my non-ds crank arm and my bottom bracket. Removed and cleaned it, trying to put it back on and can’t get it to sit flush against the bb which means there’s some play in the cranks.

Don’t remember any gaps when I first installed it, and definitely didn’t use a spacer (and don’t think there’s supposed to be one).

Any ideas?

Pic

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so in the pic your crank doesnt have the safety pin engaged so is it fully seated? It looks a little like a wheelsmfg bb that screws into itselfhowever im prettysure these do come with some plastic shims because not all 24mm axle cranks are equal yet alone bb shell widths. I'd remove the crank again, check splines and clean them incase debris is preventing the arm going on fully.

Safety pin not engaged there purely as I can’t get the arm all the way on. I’ve put the plastic cap in and tightened that but the gap remains.

I’ll give it a clean again tomorrow in the daylight but I did clean it before so pretty certain it’s not that..