Don't worry, I gotchu
Since you said no to the reset option, that leaves us to two options. The first one is to wait a little longer. The other one is to make it sleep (changing the time to make it sleep is not recommended, it can kill your Tama), which can make it grow. To make it sleep the right way, just make sure all of its meters (hungry, happy, etc.) are filled up completely, then turn off the light, and it'll start to sleep.