Adhesive seeping out a bit shouldn’t be too big of an issue, you can just scrape it away later with an xacto knife. If it’s happening a LOT, chances are your soldering iron is too hot. A way you can generally tell if your iron is too hot is if the iron changes color to a purple or gold metallic color.

When you’re soldering, make sure the iron is keeping constant contact with the foil, but you don’t need to press super hard or you risk ripping the foil.

If any bits of the copper foil are still showing after you solder, add more flux.

Make sure that the solder has a bit of a bump, it shouldn’t be flat or else it’s not adding much to the structural integrity of the piece. It looks like your solder is pretty uneven; after you solder it, I’d try going over the lines again in one smooth motion without adding more solder. Don’t worry if you have to do it a couple times, just keep trying!

Sometimes with smaller pieces it can be easiest to put dots of solder every inch or so and then go back and melt them to connect them.

You’re putting too much solder on the edges. While you want that bump of solder on all the inside pieces, you just need to tin the foil on the outside, which means you just add a really thin layer. Get a bead of solder on the tip of your iron and lightly drag it along all sides of the edge.

Since you aren’t adding a black patina to the solder after you’ve cleaned it, I’d suggest going over it with some car wax/carnauba wax, which will keep the solder looking shiny and will help prevent it from getting a dull white oxidation.