I have worries about my lack of ambition.
What makes you believe that you are not ambitious?
I'm just afraid I don't have the drive needed to be successful.
Success and ambition are nice but overrated, and spending time worrying about them only keeps you from doing things that do matter. Drop your morbid thinking about ambition and just go out and do the things you like to do.
I am doing things I like but hence the worrying. Am I just wasting my time doing the things I like?
If you are concerned about not having the life you want that's okay. If you can be ambitious about the things you find fun there is nothing to worry about.