From what you've written I deduce you are living in a rural community in the UK and plan to got to Cambridge uni to study CS. Your GitHub works are both in C.

I see two options:

1. Since opportunities for your skillset are limited in your area, you could seek out project based C/C++ programming remote or gig work. But, I think you'd be up against a lot of competition.

2. Broaden your offering to being a Mr PC FixIt guy. I don't know if GeekSquad or similar operate in your area. You could charge for results instead of the time you take.

I would recommend the second option, because it exposes you to real-world use of computers and provides an insight into how businesses operate. This level of knowledge and expertise is a valuable complement to technical knowledge.