files switched to index.php

So where, in options, you put your URI and location where your main page is located I accidentaly put in /index.php at the end. Now, every time I go to login and type in my password/username/click enter it directs to the page it’s supposed to when I login but shows up as my main page. For example, I will go to http://mywebsite/wp-login.php and type in all of my information, but it will direct to:

http://mywebsite/index.php/wp-login.php?redirect_to=%2Fwp-admin%2F

and what actually appears on my screen is my index.php file – not wordpress. I cannot login to my wordpress so therefore I cannot make changes. Is there anyway I can fix this? Thank-you.