Add a block
I think what you have is actually a 2:1. You could easily make it 3:1 by adding a block (maybe a good cheek block) forward on the boom and relocating your cleat aft so that you are pulling aft when tightening outhaul. There is no need for a fiddle block, they are typically found with an internal boom set-up.
I disagree, respectfully, with Ross ... I think for an outhaul, which I use frequently, it is necessary to reduce friction losses for an outhaul. I would consider upgrading the block at the end of the boom, maybe with a larger diameter sheave if the bearings are stiff or the block is tiny on your current setup. With good blocks, I think that 3:1 would be sufficient for your size sail plan.
To put it in perspective, I am sure that Ross still has his first nickle ...
Just saw Jerry's, which is even better ... his would be 4:1 with the block at the clew.