I don't think it's bad to not be ambitious at all if anything I'd say we have an over-supply of ambition and an under-supply of people that just want to get work done in the UK! I def think 'our' (don't know old you are but can guess roughly from having young kids) generation, i.e. growing up in the 2nd half of the 20th century, were sold a bit of a pup in terms of expecting everyone, and especially women, to have really enjoyable and fulfilling careers alongside raising families and running households as well.
Before then it was a case for the vast majority of working really hard in fairly menial or worse jobs just to survive or being 'housewives' when running a house single-handed really was a more than full-time endeavor and physically really hard work, to my grandmothers or great-grandmothers (some of whom did work, one was a secretary, one a nursery-maid, one worked in a factory fairly typical for middle or working class women of their time), the idea of having a 'career' with personal development and real fulfillment from work would have been fairly laughable (and this is still the case for many in the world today I would add). Then you had the privileged few who didn't work at all including housework or raising children as servants did that, which was the ultimate ambition at the time I guess. Whereas today the expectation is that nearly everyone even the wealthy work, the majority not in manual labour or service industries and enjoying a far higher standard of living than their ancestors, so we are in a way very, very lucky and yet I think many people feel at least bored or vaguely dissatisfied with their work and are always striving or feeling they ought to be doing more - if you've found the trick to earning a good living, being able to spend time with your children and don't find your job insufferable then I'd say you've found the golden egg TBH!
I guess don't write off the possibility of developing more of a 'career' in either your current job or maybe something else entirely later on, the young-children years feel endless at the time but they do grow up and come to occupy less of your head-space and actual time/energy, and once the childcare burden is lifted there can be a bit more financial breathing room too, you might find in your 50s or even later a job that's more of a passion for you, or you might not and find fulfillment in a hobby or volunteering or just having lots of time to yourself, all are good really!