Centrifugal casting or using steam may help with the porosity issues. Part of the issue is that you don't know the actual alloy you are using. It is probably a scrap bronze alloy and may have many other metals in it. Temperature control is critical to avoid porosity. You might be best to go back and make a ball out of it and work from there again. Put the chunk on a charcoal block with a depression in it and use a torch to melt it into a clean ball as in the instructions at the end of this post.
What went wrong with the squish is you did it too hot. You don't work copper, or any non-ferrous metal hot. Pink is way to hot for sure. Some can be wroked at dull red if you have the skills, but a hard blow or high pressure will mush it apart.
Copper and bronze should be forged to make it flat/thin - assuming it is a suitable alloy. Heat it to dull red and let cool to black, then dunk in water. Forge/press to reduce thickness, stopping to re-anneal as soon as it starts to stiffen up. With copper that is after just a little work. I find using a ball peen first and then smoothing it up with a flat faced hammer is the fastest way to spread out and thin down a thick piece.
I sent you a personal answer but thought I would post it here, too.
Copper melts at a tad under 2000°F. Depending on the source of your scrap, what you are melting may melt a bit lower or higher. You want a reducing atmosphere on the torch. It can be done in a forge or melting furnace for large crucibles, but a torch works best for a smaller amount. Clean the metal well by pickling before melting and keep the reducing flame on it at all times once you start the melt. Stir with a carbon rod. A little borax/boric acid helps keep the scum down, but don't use too much or it will make a crust over the metal. Pour into the mold as soon as it is shiny and as liquid as mercury. Give it a last pinch of flux just before pouring. Warm molds work best if not doing an investment mold.
I have never found it worth the trouble to try and cast my own copper. I always buy bars inthe size I need. In this case that isn't part of the project.