If you say you’re ambitious, I imagine you have a plan in your head of what you want to be in the future, or what you want to do, and it’s something that takes effort to do and you’ve thought of how you would get there.
If a plan is ambitious, I’d say it’s not easily done and pretty unrealistic, but could be achieved if you’re good enough.
An ambition is what you would want to work as or do in the future, like become a doctor.
I’d say I’m ambitious, because my ambition is to become a programmer and I learned how to program with online sites so I could reach that goal. However, my plan to work at a huge Silicon Valley company is quite ambitious considering I don’t live in the US and I have only ever made chat bots.