Is it normal that when I draw a line, it is not fully straight?

Check the selected line in the following printscreen. It doesn't align well with the end of the two gray rectangles.

That makes the printing not really professional. Is there a way to fix this problem?

Maybe it's not the line. Make sure the gray boxes are actually lined up?

I've already triple checked to be sure and both have identical dimension and same Left position.

When I zoom out, the line looks a bit blurry, which usually means that the line is not straight.

I've already triple checked to be sure and both have identical dimension and same Left position.

But it isn't the left position you have expressed concern about.

It is the right position; which could vary if the line width of the gray boxes is different, for instance.

Weird, I've fixed the problem using my home computer.

what was the fix?

Actually, I just redraw a new line from my home computer. Maybe, there's a small bug with my workstation.

I was currious, because it is hard to decipher from your screen shot what is the line, and what is the boxes.

Glad you got it fix.