Paint the projection screen paint, DIY-version, on the prepared and cleaned surface from the inside. Paint with vertical movements (top to bottom and bottom to top). You can overlap each roller stroke several times to achieve the most homogeneous area. Even after repeated overlapping of the roller strokes, streaks may remain, but these are naturally absorbed during drying.
If the projection paint has exceeded the unwanted surface outside the masking tape, remove the projection paint with a tissue or cloth immediately.