On an ocarina, the pitch will vary by how hard you blow. To stay on key, you have to use the correct breath pressure. You should be able to use the same breath pressure on all the notes. You can use either a keyboard or a chromatic tuner to determine whether you are staying on pitch. Eventually with practice you will develop an ear for this...or maybe you already have a good ear! 

Occasionally an ocarina will be a little flat or a little fuzzy on its top notes. If that's the case you will have to blow it a little harder to keep the highest note  on pitch.
 

Charge! Tabulated for 4-hole ocarina. If you have a five-hole ocarina, simply keep the fifth (thumb) hole covered to play this tune.

Ocarina Songs
 

Sometimes the "Ti " and the "Si "notes on an ocarina will be sharp. This will be especially noticeable when you're playing a song and one or two intervals don't sound quite right. Sharp Ti and Si notes are a common problem for many ocarina makers. There are a couple ways you can adjust this by making slight fingering changes, as shown below. You can use either one of these methods:

1. Half-holing
Half-holing can be used to produce sharps and flats by partially covering one of the holes. It can also be used to adjust pitch. 
To adjust a sharp Ti and/or Si note using half holing, try this fingering:

 

2. Alternate fingering
If the Ti and/or Si are way off, try this alternate fingering instead of the traditional  fingering for Ti and Si shown at the top of this page:

To play Ti or Si on a five-hole, 9-note ocarina, keep the thumb hole covered.