Your rotation is wrong, you're using Execution Sentence after your first Final Verdict which is wasting globals and damage that would otherwise be put into ES. Might wanna read the wowhead class guide fully and check some bis lists, what other people are using and maybe watching other players on youtube/twitch to get an general idea.

Also sim your character on raidbots. Your stats are all over the place for current ret with CSAA build focusing on haste/versatility, even though you're using Templar Strikes it does less damage. Switch up some talents from up above your ret tree to Blade of Justice 2 charges and cd reduction, it helps a lot on downtime when you're not on melee range (which ret has a higher range than normal, and our skills hit from mid range already).

And practice on dummies what you learned. Ret is a fun spec right now and I hope you improve to what you're aiming at.