Your concern is well founded but these DIY motherboards must have very good ESD protections. All you really have to do is watch how YouTube tech reviewers handle the boards they review and you'll see what I mean. They're careless as a baby with a toy and yet somehow manage not to destroy their hardware before ever getting to the workbench with it.
Odds on, you'll be fine. But good handling practice in the future will offer 100% assurance against doubts later on.
It should be alright, Ive thrown MB on my bed before and laid them on the carpet. I had a Asus Rmapage 3 extreme motherboard bought brand new in 2010, used it for 2 years then set it on the shelf for a while. It made its way to the closet for a while then sat leaning up against my desk, sitting on the carpet, for 3-4 years just the board never in a box or bag. Put it in a case fired it up and still OC'ed just as well as the day i took it out of service. I have 2 780 Ti gpus sitting on the floor right in front of my server rack waiting to go onto said Rampage motherboard. Things now a days are a lot more shielded then in the old days. yes you still need to be careful but you dont need a static clean room with a faraday cage around it to build a computer.