IMHO the whole point of this is to make sure you're saving *at all*.
I don't know what this fund's target is, but right now it looks pretty good for you. I mean, sure, there's an emphasis on your domestic market but much of that is international anyway.
IF you can be bothered to be more hands on, maybe look at 4-5 funds total: US, VXUS (which is roughly 60% developed/40% developing), bonds OR high interest savings, REITs, perhaps some additional emphasis on small cap. Do you own a house? If so that's a large chunk of your wealth in one asset, let alone one asset class, so that is diversification too.
But honestly? Don't fret. You might not be 100% optimal but it's pretty good.