This is really confusing, as I looked the whole chapter not finding anything she cut off or out or whatever，nor did she interrupt anyone. I could understand the whole passage except this "cutting in", that she redecorated her room and her dad feels proud. Could any one help me with this "cutting in" please?
Here is the sentence:
……I went to the DIY store and bought paint and new blinds, as well as a new bedside light and some shelves, which I assembled myself. It’s not that I’m good at that stuff; I guess I just wanted to see if I could do it.
I set about redecorating, painting for an hour a night after I came home from work, and at the end of the week even Dad had to admit I’d done a really good job. He stared for a bit at my cutting in, fingered the blinds that I had put up myself, and put a hand on my shoulder. ‘This job has been the making of you, Lou.’
Me Before You by Jojo Moyes
No special context here, all the passage.