There's a reason that the weight/ max horsepower is printed on a BIA sticker on your boat. My advice would be not to exceed it. It's a recipe for disaster especially in a dynamic environment like a river. Particularly THAT river.
I've spent a couple thousand hours on that river from Port Deposit to Harrisburg & above. The wind blows from the wrong direction, and it can get downright nasty out there. No place to get caught in an overloaded sluggish boat with little or no freeboard. Add cold water or high water to the equation, and it goes downhill from there.
If you're using a PFBC ramp, and a CO observes you launching or coming into the ramp & you're sitting extremely low in the water, you may get a lecture, or the guy may even write you if it looks dangerous enough.
Lighten your load or get a bigger boat