Melt Down HDPE Plastic for Projects

I've seen several videos showing how to melt down HDPE plastic containers and mold them into usable forms for projects. But I've been just skeptical enough about the safety of heating up plastic to not try it until just now. This technique made it somehow seem more doable with the addition of the press over simply heating in an oven, I think because it allows you to mush it into a blob and press out air bubbles more quickly.I want to recycle HDPE and form it into ~.25" thick squares for students to make projects on the Carvey, specifically for carving their own paths for marble mazes.  I have some 2-color HDPE to use but I hate to buy more, so I'm making my own! Here are the steps I followed.

Cut #2 (and ONLY #2) plastic containers into small chips. I used tin snips to do it.

Make sure to remove all labels and wash them out.

I sandwiched piles of chips between layers of parchment paper and let the press melt it for 5-7 minutes, then used BBQ tongs to fold it into itself periodically.

After maybe 10 minutes it becomes a sold blob, which I kept folding and pressing, folding and pressing.

I made a 4" square press mold, half inch deep.

I covered it with another 4" square piece of wood and clamped it down. I added 2 C clamps that I could screw down to compress it as much as possible to push the plastic into the corners.

I let it sit for about 10 minutes, then took it out and ran it under cold water. It's completely solid! Now I will file off the edges to flatten them and it will be ready for the Carvey!