Almost a year ago i was in school and everyone in the class was asked whether or not they believed that a certain event that took place in a play that we were studying was the result of destiny or not. I did not raise my hand because for some reason I felt shame, but in my heart i did believe it to be so. I regretted it and made tauba. But i do not know if this will bring me out of Islam. This is really bothering me, can you please tell me any duas I can read for istighfar for any sin which i may have commited in the past.