Thank you for your query at DoctorSpring.com
I understand your concern.
No, if you sleep over your cellphone for 3 hours, for 1 day. it won't have any effect or pose any risk of cancer. Some people who talk for hours on phone also have similar exposure, but it does not cause cancer.
You can completely relax and forget what happened.
If you still want to know if you have cancer, you can get a MRI or CT SCAN of the brain.
Feel free to discuss further,