2x4's, 2x6's, 2x8's, etc.. are actually 1 1/2" thick
2x4's are 3 1/2" wide
Standard framing 2x4's come in 92 5/8″, 104 5/8″, and 96″ sizes.
Remember that ON CENTER (OC) means you are marking for the middle of the stud. If you want to mark the beginning edge, subtract 3/4" (half the width of the stud) and mark there. So 16" OC studs actually begin at 15 1/4", then 31 1/4", then 47 1/4", etc...
If you need to edit the image, irfanview is a good editor you can use to rotate the image or draw shapes.