is an emergency contraception
, your first two doses is correct which theoretically provides protection for 5 days.
Till now you dont have the risk of overdose. Now stop taking the fourth one this is unnecessary. You have to understand emergency contraception has its own disadvantages.
It is only for emergency need. You should not make it a habit to take this medicine frequently.
There are better alternatives than taking emergency contraception for continuous protection, Consult your gync on this matter.