Products and Collections can take up to 72 hours to sync over to Facebook. If 72 hours have come and gone, and you're still seeing only a handful of your products appearing, then we'll want to try a few troubleshooting steps. The first possible solution is to toggle the availability of your products. If you go to the products section within your admin, select the products that are missing by clicking the small white square box, then select "more actions" then "make products unavailable."
Repeat the steps, but the second time select "Make product available." Once done, we'll want to wait 48 hours to allow for the information to sync. If the products do not appear after completing this step and waiting for the 48 hours, please let me know.