Consider that it's hard to sell anything without having an audience to sell to. What kind of job do you want? What kind of employer do you want to work for? How you sell will depend as much on these factors as on the personal experience you're trying to sell.
So, before you go trying to write up the ideal resume, consider the following:
- What sort of company do you want to work for? Do you want to work for an actual software vendor? Or do you want to work in an embedded software team (i.e. developers working at a bank, or whatever - a company where software isn't the primary deliverable).
- What size and maturity of company do you want to work for? Do you want to work for a larger, or more stable, or more structured company? Or a younger, smaller, more dynamic and less-defined company?
- What type of work do you want to do at that company? Do you actually want to just write software? Or have a more zoomed-out architecture role? Or something else specific?
As next steps, I would suggest:
- Answer the above questions for yourself. Decide what your ideal next job is, and what your ideal career path is over the next x years.
- Look at job postings and adds to get a feel for what's actually available. You're not specifically looking for your dream job so you can apply to it, first you need to do some recon and get a feel for the market.
- Look at your competition. You're in school, so this is effectively your peer students.
To answer your actual question of how you sell this experience you have, reflect how your experience applies to the job postings you found, and on how your experience differentiates you from your peers. Then, work those findings into your job search:
- Make sure you're applying to jobs you actually want, at companies you actually want to work for. If you're not sure, loop back through the above steps to refine your research.
- In your resume, and in answers during interviews, focus on describing your experience from the perspective of that employer, in terms that show how it fits that specific opening.
In other words, there isn't a single right answer to your question, since it'll depend on the specific job and employer you're trying to "sell" yourself to. If you're applying to a small, unstructured startup that just needs to get things done, you might want to focus on how you were able to perform in an unstructured environment - you could do good work despite the lack of controls. However, if you're trying to get a job in a more stable and formal environment, you may want to focus on how this "fast and loose" project helped you reflect on the true value of structure, and how you've done what you can in the meantime to hone your skills - this might sound like you're admitting that you don't have direct experience in a structured environment, but a fresh grad who actually understands why and how structure can be helpful - because they've seen a sloppy unstructured environment first hand - can be very desirable.