Why is your vang aft of your mainsheet ? Before you do anything you might want to go to the class association website for your particular boat and look at the rigging diagram there...
I wish there was an association and rigging diagram.
I misspoke: boom vang is forward of the mainsheet.
I'll read more about it when I'm not at work, but I get the gist. I do race informally and want to get better performance than I am currently. It's my first season sailing so I'm still figuring out sail shape basics but getting better. I now have things under control enough that I can actually look over the sails and rig while sailing and see what they're doing.