Hong Kong--> Beijing--> Macau as U.S. citizen OK for 72 hours?

I am a U.S. citizen that will be visiting Hong Kong. i want to make a side trip to the great wall. I understand I cannot go from HK-->Beijing--> so is it OK if I go HK-->Beijing-->Macau for the 72 hours transit Visa? I then would be going to HK after Macau. Thank you!