The next day: take bus 12 to Sun Yat-sen's former residence, Zhongshan Film and Television City and Xinhai Revolution Memorial Park, and invite people to eat seafood at Nanlang Yanshi or wonton at Nanlang Cliff. Come back to the mall at night. Your hotel is near Daxin Xinduhui, where there are department stores, supermarkets, video games, food and cinemas, and there is a snack street next to it, where you can eat anything.
The third day: there is nothing good in Zhongshan, mainly because there are many parks. Go and see Zhong Xing Road, the most beautiful road in Zhongshan. From north to south, you can go to Holiday Plaza (a small and medium-sized shopping mall with petty bourgeoisie, which is also full of supermarkets, specialty stores and delicious food) and Xingzhongyuan. By the way, you can visit our municipal government, Mingshuyuan, Zhongshan Culture and Art Center and Sun Wen Memorial Park, and you can always reach Admiralty Reservoir by bike.
And: unfortunately, it's only three days. It's a pity that you don't have a car. If you have a car, you can go to the arboretum in the South Outer Ring Road, eat pigeons in Wugui Mountain, hike in the mountains, soak in hot springs in Sanxiang, and Lihe Square and Yihua Department Store on Zhongshan Third Road, all of which are high-end consumption areas.