Memories of Holdenshire.

Remember that your wagon's momentum makes it move 20 ft. at initiative 20 at the start of each round. So the guards get close at the end of a round, attack your wagon, then you move a bit away (and move further away later in the round). Since they're not the ones moving away from your wagon, you cannot perform attacks of opportunity here.

As for attacking the guards or their horse, there are always spells, ranged attacks, or readying a single melee attack when they get in range. Yeah, this yo-yo effect is a bit weird and annoying, but it's a result of how combat works and a quirk of the initiative system.

Oil would help.

Indeed, lighting something on fire is not exactly easy, especially if it wasn't prepared to be lit up. But to resolve the action, I'd say the free use item action could be used to take out your flint and tinder and light up a bedroll, then an action could be used to throw the bedroll, I'd say a ranged attack. Then I'd give the rider a DEX save using your maneuver DC to see if he gets blinded or perhaps hindered, though the fire damage would not kick in until next round as the bedroll would need time to really "take".

Of course, if you had a spell that stipulated that it ignites unattended objects, that might work faster, but of course, it might make more sense to use it against the guards...

Finally, even without lighting it on fire, a bedroll thrown in the face of a rider could potentially blind him momentarily, or maybe even trip the horse, giving you some relief.

Yes. If you miss the rider but hit the horse's AC, I'll have the bedroll hit the horse instead, which might still help.

unroll it and throw it over the horses face to blind it

@Zariana: right now, controlling the wagon only requires the use of your bonus action, no rolls are required. This still frees your regular action for something else, like casting a spell.