i can't complete the yoga event on saturday, what i need to do to finish this part?
Is that:
1: The one with all three girls
or
2: The one with Mom alone?
1: You can't. Not YET, anyhow. In a future update, the Gym will have a yoga room. Maybe then.
2: How far along the path are you?
If you've only gotten as far as Mike prodding her arse with his boner, that's it for a good long while.
Continue working on her through other means and new events will open and guide you towards finishing the event.
Claire/Mom also does yoga throughout the week around 6AM IIRC.
Be mindful of "I should work on" style help texts. In some instances you can still increase the Love stat but nothing else.