I think I have mouth cancer in the corner of the inside of my mouth?

See below. See your dentist immediately. If problematic, you may be referred to an oral surgeon for a definitive diagnosis. Don't wait.
Mouth cancer. Important that you see your Dentist or a specialist Oral Surgeon immediately for an examination. Risk of oral cancer is very low, but increases with smoking (anything), alcohol abuse, age, chronic irritation. Not a DIY problem, you need professional management. Please call a Pro.