Legal Question in Real Estate Law in California

Almost certainly not. It would require a survey to determine exact limits, but when lots are created and streets and sidewalks mapped out, the public right of way is usually wider, sometimes much wider, than what is developed. This allows for future widening without the need for eminent domain proceedings. So what you think is your property limit, probably is not correct, and the City probably just extended the sidewalks and ramps into property that the city already had the rights to. That is consistent with what they are saying.

As for "ownership," it is possible that your property line goes to the middle of the street, and then the city has a right of way over your property for streets and sidewalks, or it is possible that your lot line just extends up to the city's public way property, and because the original sidewalks didn't fully occupy the right of way, you thought your property extends farther than it does. But that really is a distinction without a difference. As long as the city is within its right of way on the relevant parcel map, they have the right to do as they wish with it and you do not.