A good way to
get reliable cuts with your circular saw is to take a few minutes and make a guide. Start out with a relatively flat piece of ½" or ¾" plywood, about 8 to 10" wide by 8' long. On top of this, mount a 2" wide piece, about 5¾" from one edge. No need to take any great pains at establishing the dimension. + or - ¼" is plenty good. The important thing is to make sure the 2" wide piece runs in a straight line from end to end. Glue and screw/brad together and let the glue cure for an hour ot two. Now, clamp the assembly onto a pair of saw horses and get out your circular saw. Assuming that your blade is on the right side of the saw, set the blade depth to cut through the bigger piece of plywood. Put the saw shoe against the 2" wide strip which is your guide, and saw the length of the panel. Now, when you need to cut something that doesn't fit well on your table saw, make a pair of marks, slide your saw guide up to the lines and saw with confidence. You will get a perfect cut everytime now. Just remember to clamp the jig to the piece you want to keep. Kind of like standing on the tree side of the branch before you cut.
Ed