Many people ride with the rub rail at water level or even lower. We do. It sounds like you could put more weight on that boat, honestly...
Weight at your own risk though and be careful when driving.
I haven't heard of anyone swamping a surf weighted boat in the last few years, but that doesn't mean it hasn't happened.
My wife used to worry and not want to weight the boat too much. No she is wanting to put more and more weight!!