The mass of the universe is not distributed evenly, so it gets really complex. However, as a semi-qualitative assessment, I can say that the vast majority of the universe is just empty space, so you should be fine for the most part. However, the longer you allow the top of the lorry to scrape the edge of the observable universe, the more likely it is to hit something.

Think of it like throwing darts. The more you throw, the more likely it is for you to hit the bullseye. If you keep on driving your lorry for an hour or two, the top has already swept across an enormous arc and probably plowed through multiple galaxies along the way. Keep on sweeping and eventually you’ll smack into something.

[–] Natanael@infosec.pub 2 points 1 day ago

There's actually math for this where you look at the distribution and distances of mass and calculate probability of hitting something based on distance (created to calculate things like how far you can see in the woods)