I finished the lower shell part!
I ran into some issues with the button placement because I didn’t think about it when designing the main PCB. I placed the button too close to the edge of the PCB, leaving only about 3mm of space between the button and the wall of the shell, as shown in one of the pictures. Since I already have the PCB and I don’t want to order a new revision just to move the button, I will use a different button on the side of the power bank that I will solder to the original button pads with wires. It’s probably not the best solution, but it should work.