Do I have mouth cancer if I have white patches on my cheek?

Very unlikely. Mouth cancer can present rarely this way, however it would b a rare presentation of a rare tumor. There are many more things likely to cause what u describe aside from cancer. If u are concerned and they have been there awhile or are causing issues, i would see both your dentist as well as your md.
Not necessarily. White patches on your cheek can be a number of things that is not necessarily cancer. Go see your dentist right away.
Leukoplakia. Possible leukoplakia which can be pre-malignant. See oral surgeon or ENT doc for assessment.
Possibly-need biopsy. It is impossible to determine if a white lesion in the mouth is cancerous. It is suspicious. It can only be confirmed with a biopsy.