To serve, remove raspberry sauce, thick watermelon disk on the platter, and the mixed fruit from the refrigerator. Pre-slice the watermelon disk into 8 wedges, but keep together to form the base of the cake. Place 8 small scoops of ice cream onto the watermelon cake. Top with reserved berries and watermelon balls. Drizzle with raspberry sauce and garnish with mint leaves. Serve immediately.