My boss wants me to design and paint our workplace. At first I agreed, but now I changed my mind. How do I professionally tell my employer?

...and would I be the asshole in this scenario?

I have no experience in interior painting and decor or graphic designing.

My boss just saw my watercolor art one day and liked them, so they asked me to paint their whole business, including making graphic designs, too.

I realize that this whole project is way over my head. So I want to decline.

But my boss is tight on money, so it seems like (or at least they act like) I am their only affordable option. Honestly, at first I was not going to charge them for my art.

But this would be just too much work. I am in college too and have little extra time on my hands.