resize linux root file system

mount and fstab.txtDear Experts
I having centos 7.8 on google cloud platform space got filled up hence increased the space from 50GB to 250GB by going to google cloud console and Disk Management page edited and increased the storage capacity
Then login to VM and executed the
#lsblk
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda      8:0    0    50G  0 disk
├─sda1   8:1    0    200M  0 part /boot/efi
└─sda2   8:2    0 49.8G   0 part /
-----------
# growpart /dev/sda 2
After this
#lsblk
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda      8:0    0    250G  0 disk
├─sda1   8:1    0    200M  0 part /boot/efi
└─sda2   8:2    0 249.8G   0 part /
 
After this when tried to resize I am getting following message
#resize2fs /dev/sda2
resize2fs 1.42.9 (28-Dec-2013)
resize2fs: Bad magic number in super-block while trying to open /dev/sda2
Couldn't find valid filesystem superblock.r

1. Attached mount and fstab output.  

2. Please suggest how to resize, should I have to unmount root if yes  then please help me with steps, if umount it’s not required then what steps to be done so that the resize gets updated,