Seems you partitioned your disk in a different program, not fdisk.
If this is an empty disk, then better to start over
sudo fdisk /dev/sda
Then d and Enter and repeat until it say Partition 1 has been deleted.
Then n and Enter, p and Enter, then hit Enter until got a prompt
Command (m for help):
Now q and Enter.
Create a fs:
sudo mkfs.ext4 /dev/sda
I fixed the guide to use a whole disk.