Our 5.5 month old hangs very close when off leash, especially in an unfamiliar area. I'd try to go to a place, or a time when few people will be around. It helps to be able to see a ways, time to leash up the dog.
Carry a few treats with you. I also don't do a lot of calling, unless I mean it. I like to use 'body language' to influence and control the dog. That could be you stopping, facing a different direction, or walking the other way. I also hide behind a bush at times to develop the desire for the dog to look back and see what's in store next. That's not a big issue now since Mya hangs so close.