Don't give up. It's very fulfilling going out on your own and pursuing something, be it a "hobby business" or a full-time gig. Regardless of how small or large you're thinking right now though, you should write up a business plan. I know this may sound silly if you only intend to do this as a hobby and aren't expecting a large return of money. It doesn't have to be incredibly detailed either. The main function of the business plan is to display your goal, how you intend to reach it, and act as a guide for you so you don't forget or miss anything.
I'd recommend talking to the store owner and finding out exactly what sizes, accessories, materials, etc. they want. Then draft up an estimate for their approval. Make sure you specify when and how you want to be paid too.
This forum is also a network to assist you. You can ask people for ideas and opinions before you go and spend money on anything first. This is a huge benefit. Not all businesses have that going for them.
If you have any questions regarding starting out feel free to pm me.
Good luck
