I like to use aluminium foil that's about twice as thick as the usual stuff for kitchen use, but still far thinner than a coke can. I get it from some packaging, but hardware stores could have something similar. Just put it on a relatively soft surface (piece of cardboard), and use a thin sewing needle to drill a hole by holding it between thumb and middle finger and resting the index finger on top (no pressure, the weight alone is enough!). Finally, I just turn it around, drill again from the other side and sand both sides very carefully. Depending on the drilling time, pressure and needle size, I can get almost perfectly round holes from 0,15mm to 0,6mm almost every time.
And please don't worry too much about the pinhole size and shape. 0,56mm might be the optimum for your focal lenght, but you'd also get a (less sharp) picture with any other size of hole. 50% more or less don't matter much at all. I tend to use a size, that gives me a usable aperture around f/150-200, not necessarily the "optimum size". Same for the perfectly round shape... sure, it gives the sharpest pictures, but a few microscopic pieces of metal won't make your pinhole unusable. Pinhole cameras are very simple devices - no need to over-engineer it.
...and that "blurry and uninteresting" is part of pinhole photography. You just can't get the same shaprness as with a lens. And just like any other camera (or tool in general), a pinhole camera needs some skill and experience to use properly and get interesting results. An ultra-wideangle can help with this, as it gives perspectives, that are usually not possible in lens-based photography. I love my tiny matchbox pinhole cameras for 35mm film... they're even less sharp than any 4x5, but I came to like the effect. Just remember that this is not "normal" photography, it's a completely different kind of taking a photo.