You say in the video to apply the sealant to the brush, don’t dip the brush in the sealant…though the video shows the brush being dipped into the sealant.
Cannot tell but it looks like you put sealant on an existing storefront frame window sill that has drainable sill flashing. You have just blocked off the window drain and now water will go over into the wall cavity at the ends if there is no end dam or back into the interior ledge.
