Puppy stops while walking to go potty?

We have a 5 month old golden, and we're trying to train her to go potty outside. We've been trying to be more diligent in taking her out on a sort of schedule. However, our yard doesn't have any grass (we're renting), so we take her to a nearby park that's about 3 blocks away. However, she often sits down once we go outside and refuses to move. Even when we manage to walk for a bit, she will choose not to move again and want to go back home. So I've often had to carry her some of the way to the park or drive there, after which she walks for a bit on the grass and does her business.

Any tips to have her walk all the way to the park? It's a hassle to try and drive there when it's only 3 blocks away… I've tried to lure her with treats, but it only works a few times along the way. She also gets frustrated when I don't go back home when she wants to.