Q.Will temps in the mid 30’s hurt my strawberry plants
I got impatient and planted my 20 bare-root strawberry plants in the garden 3 days ago. It has been gorgeous out! Now, after an 80 degree day, they say it will be in the mid 30’s tonight! Can I throw a sheet or blanket over them for tonight? I don’t have plastic.

Yes, I would throw a blanket over your strawberry plants.
Make sure you do uncover them though as soon as temps improve. Leaving them covered in bright sun could cause them to burn.
https://www.gardeningknowhow.com/edible/fruits/strawberry/growing-strawberry-plants.htm