Yes! It’s doesn’t really matter if the viewfinders are exactly like described in the book, as long as it’s something transparant with the horizontal and vertical lines. You’ve done this very well.
What is so cool is that this method conveys depth. It really looks like your hand is “coming out of the picture”, if you know what I mean. Getting a sense of movement in a drawing is one of the most difficult things to do. And here you’ve done it!
One thing that will make it a little easier to work the exercises with this guideline method. Try to place the subject you are drawing a little more in the middle in such a way that the empty space is evenly distributed in all four rectangles. This empty space, also called negative space, is an important part of learning to see with the “artist eye”. I’ll post an example of what I mean later in the morning.