Here are a couple excellent images of the SY border crossing and FMM info. Stole it from another forum and I wish I could give proper credit but thank you TMW from Baja Nomads.
This may help in getting your FMM.
Follow the red line to the area to park. Follow the blue line and go inside the bldg and walk to the area between buildings. The office is to your left. Fill out the paper work then go back inside the building to pay at the bank. There are two banks one on your left as you came into the building and one on your right as you went out near the FMM office. I'm not sure if you can pay at either as I've only used the one where you come in on the left. Anyway pay then go back to the office and get it stamped and signed.
Follow the yellow line to the toll road. Remember to stay right when you leave the entry gates.
FMM TJ.jpg
FMM TJ2.jpg