The 9th bearing will fit, they just need to ride on a wider circle. The angle of the races just caused them to slide down towards the middle.

Use grease on the races to hold in the 1st 8. Then push the cone down onto the bearings and turn it. You'll see that the cone squeezes the bearings out into larger diameter circle. The grease should hold the bearings at this wider circle. Insert 9th bearing and re-assemble.