I too bombed in second year of my degree. Looking back I can see that it is the "dip" (there's a book by Seth Godin on this topic) in your academic progression. Your references to not knowing enough come across as the imposter syndrome. It seems to be common for people with high standards.

Based on my experiences I would suggest dropping the math major and concentrate on graduating with the CS major. Do they have 3 year degree courses or only 4 year? In other words make your goal the MVD (minimal viable degree).

With the degree and 3 years experience you would have better employment prospects than by dropping out and just relying on your experience to date.

If your intellectual interests require it, you can always do some post-graduate study on a part-time basis. Having spent some time teaching and researching in academia, I would suggest doing some in-depth research and talk to people before committing to that path. It can become quite bureaucratic and grants focused and thus more stressful than the majority of jobs in commercial settings.