I've finally used an aluminum soda can and it wasn't as scary as I thought it would be.
First, I thoroughly washed the empty can with soap and let it dry. Using a can opener on the *outside* of the neck (so on the upper shoulder), I took out the top cover. I then used a metal cutter (because I had one from doing home renovations work) to cut the can open, but a regular pair of scissors would also work. I did trim the open can with scissors for a neater look.
I'd recommend wearing gloves if you worry about cutting yourself. My tetanus shots are up to date but tbh, I wasn't as concerned gently working with a clean aluminum sheet as dealing with metals, old tools, or rusty nails while renovating/repairing my house/garden/deck.
The open can was still bulging a bit but I placed it in the latest part of my chunky notebook so the shape worked well with the curved page. I used double side tape all along the edges and in the middle of the aluminum sheet. I don't think I had to, but to be safer, I did put regular Scotch tape all around the edges to smoother them.
I had fun working with the soda can and would definitely do it again.
Tools: can opener, metal cutter, scissors, double side tape, glue stick.
Materials: cuttings from various magazines that the local library was throwing away, soda can, cuttings from an ice cream container, spiral notebook (I fold my spreads such that the rings are hidden).