It won't have a gap once you tighten the axle nut, the hub ends up with a solid stack of bearings and spacers between the axle head and nut.
The hub is only located along the axle by the retained bearing (with the threaded ring holding it against a shoulder). The opposite bearing is free to slide in its bore to meet the middle spacer.
If the floating bearing is super tight in its bore, open the bore slightly with something like 600 wet/dry paper until the bearing can be moved in the bore without extreme force.
Installing it on the axle poked through from the other bearing helps avoid it getting tipped in the bore and jamming, that will damage the bore if you force it.