Hello & welcome
having gag from complete denture is a very common problem, for one to two months you have to struggle, than you will get adapted but as you are saying that this is very difficult to close the mouth even than you can ask for medications for this & can opt to visit a doctor because this is a psychological problem mainly.
In the mean time start doing some of exercise like whenever you wear denture start doing deep breathing through nose, movement of your toes & try to deviate your attention, surely you will get benefits.
rest about looks & color of denture you have to talk to your dentist
, because we frame dentures to simulates patient natural look.
thanks & take care