A similar thing happened to me in the '70s when I was about 14-15. No phones, of course. I managed to evade him and he didn't see where I lived. I never saw him again.
I DID get the plates and the make/model of the car, only because he followed me for a long time, and he would go ahead and then wait for me to pass again.
The only thing I would suggest you might have done, that I could have done, was immediately double back towards wherever you could have felt safe. In my case I was leaving the park after playing tennis, and my only choice would have been to go to my tennis partner's house and try to lose him in traffic on the way. Where I lived there was no traffic, but I could have lost him on the way to her house and ducked in somewhere.
I think I did everything it would have been logical to do based on what I knew at the time. I spent the next year looking for that car! Never saw it again. If I were you I'd keep a lookout too, and don't wait...just call 911.
Don't feel bad. You did everything it seemed reasonable to do.
Karen
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insidious ungovernable cardboard