I usually get result of path that getting cut in the part that been overlapped by another path by using Path > Difference, but today I get weird result by using same method just like this.

Can I still fix this?

One object is not a filled path. I'd use Stroke to Path before the path operation.

Oh my... I forget to make Path by Stroke to Path. I thought i can do the boolean operation just by using object that had been turn to Path yet. Thank you for reminding me