If you try playing the highest octave of the C major scale starting on hole 7, you will find that the note B (the 7th degree) is missing, so you get C (1), D (2), E (3), F (4), G (5), A (6) C (8).
The following example contains three octaves of the C major scale (apart from the missing B note), which is the complete range of the C harmonica. All ten hole diatonic harmonicas have a range of 3 octaves regardless of what key they are tuned to. When you play in the key written on the harmonica (in this case C) instead of cross harp, you are playing in first position. As you learnt in lesson 2, cross harp is often referred to as second position.
As you play this example, try to mentally name the notes as you play. If you have trouble, think do, re, mi at first, then name the notes. Once you can do this, play it again and mentally sing the scale degrees as you play. Remember that the octave of C (degree 8) is equal to degree 1, so count each new C as a 1 rather than an 8. E.g. 1,2,3,4,5,6,7,1,2,3,4,5,6,7,1,2,3, etc. It is important to remember that scale degrees are purely theoretical numbers which relate to all instruments regardless of their playing techniques. Do not confuse scale degrees with the numbers of the holes on the harmonica.
This melody is played right at the top of the harmonica. Learn it and then analyze the degrees. If you make a habit of this, you will learn new melodies much quicker.