Issue joining the spindle carriage to the Z-axis rail

This is my first assembly. Was doing great with the build so far, but ran into a problem that I’m hoping someone here can help with. I did a quick search here, but didn’t find any thread that seemed to match.

So step 9 of “Gantry - Z-Axis”, Attach spindle carriage to the z-axis rail. The instructions say, “Starting from the bottom of the Z axis makerslide, slide on the spindle carriage. Make sure that the V-Wheels ride on the makerslide rails that stick out to each side.” This seems like it would be dead simple. Just roll the carriage up the rail and attach it to the delrin nut on the leadscrew.
But, this doesn’t seem to work. It’s as if the z-axis rail is a mm or two too wide and the v-wheels just won’t roll along the rail.
I’ve tried really forcing it, but I’m afraid of either damaging the wheels or having the whole thing slip out of my hand and slicing arm open on the bottom of the rail. It’s not a matter of needing to adjust the adjustable wheels. Both sides line up with the rails just fine. Again, it’s as if the z-axis rail itself is too wide to accept the carriage onto it.

Before I try really cranking on it again, is it supposed to be this difficult to roll the carriage up the rail to be attached?

You may have to rotate the eccentric nut/spacer so that the wheels move outward or just loosen the wheels and bolts a bit and tighten them up later. I would probably get them adjusted all the way out then readjust after it’s attached.