A "hacker" in quilting is the person who just picks up a strip of fabric and starts to sew it down on the border. Never pre-measures, just sews it down and then "hacks" (cuts) it off.
Not the way to do it.
Press your quilt top well. Take the quilt top to your table, lay it flat, and with a measuring tape,
measure through the centre of the quilt from one side to the other. Write the measurement down.
Trim the selvedges from your binding strip and then cut to the exact length that you have measured. Finger press the middle of both the top and the border. Pin the border and the quilt top together at this point.
Then pin the two corners. Complete pinning the entire side of the top.
Do the same on the other side.
Once the borders have been sewn down, press and then measure the quilt top through the middle from top to bottom. Attach these two side borders exactly the same as you did for the top and the bottom. Always finger press the centre and place your first pin there. Then the two corners and then the rest of side.
You really just continue on with each border in the same manner. Measure and be accurate.
If you have to join the strips for the border, use a 45* angle to join them. This way the join is not as noticeable. Then when you sew them on have one join near the top and one near the bottom. Your eye won't travel to the join when they are placed at opposite sides.
And guess what? Your quilt is probably square too.