Mostly Flat Object appears to stick to the bed, but warps after 3 or 4 mm

As the title suggests, I'm trying to get an object to print, it is a case for an Arduino project I'm working on. It's mostly flat, but won't stay stuck to the bed long enough to finish printing. I have Filetted all of the corners, hoping to remove some stress, but that didn't help. I've attached the STLs for the case. If anyone has any suggestions, I'm all ears. I'm working with an Alunar A8, It's an i3 clone with a 220x220 heated bed.

I will try that, thank you!