Word order
In English you might expect the Greek to look like this.
ἐστιν μου διδάσκαλος
But Greek word order is different from English, in some cases very different. Many adjectives follow the word they modify. μου will always be after the word it modifies, and in your translation you will always put it before the word it modifies.
ἐστιν διδάσκαλος μου