Lining paper filler combination for removed fireplace

[Clarabel]

Hi
I am an amateur decorator and recently had a plasterer remove a fireplace in my 1930s house. I was not best pleased as he used plaster board rather than bricking it up and just cut a square in the lining paper leaving rough edges so I cannot just paint over it.
My question is how can I patch in the rough edges if the lining paper to make it look ok for repainting? I absolutely know I should strip the paper off but do not have the physical or mental strength to do this and have a very tight time schedule to get it decorated.

Should I sand the rough edges and use some sort of filler?

Any advice appreciated (just don't tell me to strip the rest of the paper off please!).