L-sit

Lift your legs up a couple of degrees higher, shrug your shoulders down more (I'm not sure if this is the proper terminology, but you want to be actively using your shoulders to press your body upwards). And work on turning the rings outwards.

Lift legs up more - yes definitely. I've always had tight hip flexors and hamstrings so I am actively working on improving this.

Shrug shoulders down to push body up - yes. Didn't think about it when I was doing it and that's a good suggestion too.

Turn rings out more - I think they may be a little more turned out than they appear in the photo because of the angle it was taken - hard to say, plus the way they're strapped up makes them a little less conducive to being turned. I wish I had a head on shot to see what it would have looked like from that view. I do have pics of other static holds taken the same day where the rings are turned out.

It looks like your elbows are slightly bent too. Try and lock those out.