Hi, welcome to LQ!
It's quite possible that when you re-partitioned your drive it created new UUID's for the partitions.
Your boot loader is using the old UUID.
On a bare-metal install, I would use blkid (block ID) to list all the uuid's and the edit grub boot parameters and boot (f10)
after that you will need to edit grub again,
but to make it stick for a reboot you'll need to edit /etc/default/grub and then execute update-grub.
Using a Virtual Machine, I hope this gives you a starting place.
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