GIMP Window Changes Size on Any Action

[Jeremy_Ray]

I use Linux, but I'm far from a developer level of knowledge.  All this snap, apt, flatpack stuff - it seems like there's a new one every day.  I've got too many other things going to keep track of it.  I was hoping the issues with snap were solved by now.  

Is this error message a real problem?

Code:

Reading package lists... Done
E: Could not get lock /var/lib/apt/lists/lock. It is held by process 3120 (packagekitd)
N: Be aware that removing the lock file is not a solution and may break your system.
E: Unable to lock directory /var/lib/apt/lists/

I got it after sudo add-apt-repository ppa:ubuntuhandbook1/gimp-3 and sudo apt update.