She IS small, sadly. It looks like you've only started to feed her nutrients this week and that's why she's so small. You should have been giving her grow nutes about week 2 or 3 and she'd be much bigger. At this stage, she needs bloom nutes and won't do well if you start giving her grow nutes so don't think about that.... She looks like a very healthy plant and that's great.... she'll give you a small harvest but you should be grateful for what she gives you and try again... She's a lovely looking plant!
Good luck!