Help! Can’t get stain thick enough?

Hi! I received a piece with some scratches on it so sanded the side down and applied new stain on it- my sister gave me the original stain so I know the color is matched. For some reason the stain is not sticking like the rest of it which is making it look much lighter. The original stain feels much thicker, almost like a paint, but when I apply a new layer it doesn't seem to be changing anything. I asked my sister who did the original stain job and she has no idea how she originally did it to get so dark.