$10/$20 Plays itself or I donked it up?

[Rosslex]

I have 18 outs no? (7 diamonds, 2 queens, 3 K's, 3 J's 3 T's) if I presume he has the flush already.

Now my dilema is how do I get paid maximum if I hit river diamond or fill up?

Knowing he is calling if I push turn does that still make it correct tp push to maximise EV? I would essentially be betting $968 to win $1308. or can I consider my $200 call already in the pot and therefore be betting $768 to win $1508 thus making it the correct play getting 2-1 pretty much?