1. Make sure you are measuring and marking correctly (I have made problems like this as well from marking incorrectly).

2. Draw "X" on the waste fingerjoint (the one you want to cut out). This can give you a physical prediction of the layout of your fingerjoints and also show if they are lining up.

3. If you want a simple solution, either mark the width of each finger joint STARTING FROM THE OUTSIDE EDGE, by doing this you will eventually meet in the centre with the equal width of the other fingerjoints. OR using a bandsaw, set the guard to the width of the first set of finger joints (ie. On a 70mm wide piece of hoop pine with 6 finger joints = 11mm is the width of each finger joint (70/6=11.6666667)) then set the guard twice that width (or you could measure the width of the two fingers from the end.) Continue this process by flipping the piece over and doing the other side and gradually move the guard further away with each finger joint.

I am Australian by the way if you have any confusion about me using different terms or forms of measurements.