There are different methods for squaring off bag bottoms. I am going to try to explain my method which may or may not be like anyone else’s.
I am not going to go through the process of getting to this point. Only from this point to make your bag bottom.
You will need:
Your bag with side seams and bottom stitched together
Ruler that is at least 4 to 6 inches X 4 to 6 inches. (mine is 4 X 13)
At this point the bag will look very similar to this. Wrong side out and flat. Very flat. Pressed to the point of maximum flatness. The goal here is to be able to see the crease in the bottom.
I then mark this with a fabric marker, pin and stitch opening that seam to eliminate bulk. I usually sew across, pivot and sew back on this line.
Then press and turn right side out. You can trim off the triangle or leave it. Whichever method you prefer. Poke out the corners and press again.
Please give input. I would really like to know if there is something that is not clear and feel free to contact me with any questions.