Sounds like the clutch needs adjustment to me -
https://faq.ninja250.org/wiki/Adjust...e_clutch_cable
What is the hot idle speed set at?
The carbs/TBs may need to be synced or there may be maintenance items (air filter, valve adjustment) that may need to be done.
I would also check the kickstand and clutch switches -
https://faq.ninja250.org/wiki/Unders...afety_switches
More general info -
https://faq.ninja250.org/wiki/Ninja250_Howto
It dangerous to ride like it is, so if you can't get it sorted I would take it to someone that can.