Pearl Feng Xuan, look at the spots and patterns on her body. If there are many messy spots and patterns, it means she is a mother. Another way is to see if its forehead protrudes much more than its nose, indicating that it is male.
If it is just 20 days old, there should be no way to identify it. You can't really tell the difference between male and female until it is one year old.
I hope you can be satisfied! ~^_^~!