No worries. Depending on what time your Tama was born, it can change at either age 3 or 4. If you started it early in the morning, it will probably change at 3, and if you started it in the afternoon or at night, it will grow at age 4.
do you pause it a lot? my tamagotchi took about a mounth to evolve because I paused it a lot. try pausing it a little less and see what happens. :furawatchi: