I think you're OK.
When you put it in gear the prop spins and puts resistance on the engine causing the rpms to drop.
Mine is a carbed 200 that idles around 1000 in neutral and about 700 when in gear.
When it gets to idleing rough and harder to start, change the spark plugs. I change plugs once a year.
You got a good boat and motor combo there for sure. good choice for a first ride.