configuring config.yaml:8:18 with error in incosistent indentation in ubuntu server 20.04

I see several incorrect items in your yaml file. I suggest that you consult:

cat /usr/share/doc/netplan/examples/static.yaml

Carefully amend your yaml to match:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp3s0:
      addresses:
        - 192.168.0.243/24
      gateway4: 192.168.0.1
      nameservers:
        addresses: [192.168.0.1,8.8.8.8]

Proofread carefully twice. Save and close the text editor. Follow with:

sudo netplan generate
sudo netplan apply