I think it may look a little off because the arrow usually rests on smth (the ref you have has a special hold thing but the art version doesn't) so you may want to try putting the arrow resting on the index finger. A lot of times people wrap their index finger around/on the arrow to keep it in place next to the bow while they draw so you could try that too. Another thing is the perspective for the stance you're using makes the bowstring look relatively straight instead of bent due to resistance. Maybe tilting the bow/hold to be more vertical (the knuckles more perpendicular to the ground like in the ref) could help? Of course there's lots of different bow holds/styles and I'm definitely not an expert so don't take this too seriously lol
side note: Everything looks super amazing and I'm really excited to play!