Hey Mate,
It could be different reasons why your plant is still so small.
You should provide more information about your grow, so the community is able to give you smart and reasonable tips to help with your problem.
How often do you feed them?
What substrate do you use?
pH ok?
Which lights and what power?
Temperatur during day and during night? And so on...
With such poor information you won't get propper answers.
Best of luck for your grow.
Au revoir✌️
OimRausch