Nice examples from columbia93. You can also look at pictures of real creeks since that's what you are trying to emulate. It might just be the pictures, but it looks a little flat to me. That's the reason the second example from columbia93 looks better with the mulch. Even though you aren't using it for drainage, it's illogical for a creek to flow on the same plane as your lawn - so it will always look like a gravel path if you don't emphasize the depth.
I also agree ending it at a boulder is odd. I know there has to be a beginning and end, but the shape looks more pond-like when I can easily see the beginning and end. I would want it to run the full length of the bed and seem to disappear out of sight around the end of the bed.
I feel like a dry creek bed requires a good bit of design on the front end to make it look natural. You need 2-3' of width along a good portion of your backyard + the plants and boulders to tie it together. If that doesn't work with your existing landscape plan, maybe there's another solution for your spot behind the patio.
Q