Sri Lanka? Travelling?

There are 5 of us doing volunteer work in Galle from mid August for 2 weeks, then our plan is to travel by bus to Arugam Bay and stay there at Rango's beach hut for 6 days, leaving us with 13 days of our trip left! We would love to travel to Kandy, and we want to see as much wildlife and culture as we can! We also want to go to the Waterpark in Colombo... can anyone suggest what we do and where we stay for the last 13 days of our trip? thanks