One Simple Step Could Prevent Parchment Paper From Curling
Parchment paper is basically heat-proof, non-stick, food-safe paper you can fold and manipulate into lots of different shapes. It can fit in muffin tins as well as along the walls of cake pans; You can even craft a makeshift piping bag if you really need one fast, per The Spruce Eats. But sometimes you just need the darn sheet to lie flat.
Usually parchment paper comes in thick rolls (like plastic wrap or aluminum foil) so when you tear some off the roll, the sheet is inconveniently jagged. One easy method to flatten out the paper (and maybe let off a little bit of steam as well) is to simply crumple the paper into a ball and then flatten it out again. This will allow you to more freely manipulate the paper as it will now be easier to mold into shapes and to position flatly on a surfaced.
It may not look as pretty as it did before, but no one will come looking for it. No one will even miss it.
Why it works and alternatives for your parchment paper
Parchment paper is coated in silicone, which gives it its kitchen-specific qualities and a certain amount of rigidity. The paper wants to keep its curved shape from when it was on the roll and crumpling the paper up gives it a whole bunch of new curls that go in every which direction, thus making it easier to manipulate. Crumpling the paper does not undermine the integrity of the parchment paper at all and it will still function as it should.
If you're a parchment paper sympathizer and can't bring yourself to crumple up your sheet, there are some other, less satisfying alternatives. Real Simple suggests brushing some oil onto the edges of your sheet to convince it to stick down onto a surface or to use oven-safe magnets and/or weights to ensure that the paper lies flat. You could also pre-cut your sheets and keep them stacked and weighted together to try and flatten them out over time.