Now that you have a sled large enough, and with enough hold-downs to support both the stock and the cut off, you want to add a shield to make it safe.

Fasten a 6" 2x 4 block on each end of the sled, centering them on the axis of the slit. Get a piece of plywood, or plexiglas which is the same length as the sled, and six inches wide. Fasten that to these blocks. It will bridge the entire slit, keeping sawdust out of your face, and making it hard to get your fingers close to the moving blade.

You've got most of this already so going with a base which is big enough to give you room for these added features should be an easy upgrade. You get stops, an extra hold down for the off cut, a fence with more support for the stock near the cut, and a safety shield. If you want to later add sides to that shield you can connect a vacuum tool and collect the sawdust as it is being made.

Hope this helps.

PGJ