I Accidently Stepped On A Dog Last Monday And I

I accidently stepped on a dog last monday and i am not sure wether he bit me back or not.
to avoid risk, i took anti-rabies injection on friday.
Is it safe or too late to have injection after 4 days ?
I mean what is actual duration to take injection to avoid rabies infection after the dog bite ?
Is it safe if i took these injection after 4 days of accident.