Two days to visit the Great Wall? I think you can try Jinshanling or Simatai. They are the wild walls but has more to see. My suggestion is you go to the wall on the first day, but not climb it, instead you lodge in the surrounding farmhouses where you can taste the authentic Chinese village food, have a nice rest in the farmhouse, and start to climb the wall on the second day. All Great Wall trekkers would prefer to be arranged like this.

Oh, forget to say, Beijing is windy and has a large temperature difference between day and night in April. So you'd better bring some warm clothes, and also, umbrella is necessary.