It's not going to win any speed records, but its not that slow. 3kts is just about the speed limit on the canal and you can only do 4kts on the Thames. Even with the max HP for your boat its unlikely to plane because of the floor configaration, max speed would only be about 6kts.
One of my 1st tenders was similar to yours, a 2.4m slat deck with a 3hp engine, it was a long slog between the dinghy pontoon and some of the moorings in Salcombe. You need to take care with the tide and avoid peak flow periods, make sure the weather is settled and take safety kit and life jackets.
Boats are great, but it doesnt matter what boat you have, you always need
a bigger/faster/newer one