Hi Linda, Look the good news is you can just disregard it. The grass will soon crowd it out and it's going to die off anyway when it goes out of season. I wouldn't do weed and feed at all.

the important thing at this stage is not to cut too low, and be absolutely sure that the young grass is sturdy enough and wont be pulled out. Cape weed thrives in areas where theres not much nitrogen so good lawn maintenance of regular feeding and mowing will eliminate it. and at this stage it's probably doing more good than harm, though unsightly i know. But it's stabilizing and shading your young grass. use the time for something more productive, or restful.