That tarp is probably trapping heat, and it's so close to ground. A tree provides layers of shade from higher up, but that's not an option. I once had a half-circle pen made of trampoline, so I had an arch. I covered it with two layers of sun shade cloth and no rain got through it. That would trap less heat than a tarp yet still provide shelter. IT can be fastened with butterfly clips specially made for sun shade and bird netting, or if it comes with grommetts it can be fastened with bungees.