You’ve got a face there, but some of the mesh needs fixing. There’s a section above the corner of the mouth, and of course the highlighted spot on the cheek near the nose where the loops get a little wonky. Use the Loop cut tool (Ctrl-Rkey) to show you where the loops are. They should be going around the mouth and around the eyes.
Rebuilding can be done by removing one vertex at a time (so you don’t loose the shape) and reconnecting remaining vertices in a loop fashion. If you need extra vertices, you can either select an edge and subdivide it (Wkey>>subdivide) or extrude a single vertex.
Extending loops can be done in sections: decide where the new loop will connect, and then extrude one less vertex. You’ll have a gap, which you can fill by making a face.