" Did you drill the two pieces at the same time or individually?"
Drill flip drill.

Once you have drilled all the holes and added the tooth picks [for a first try] the tracks may not lay down flat, if this happens you will need to dill out one side just a little bit [1/32] more so the tooth picks have room to move around just a tad.

https://www.lumberjocks.com/threads/blog-post-index.331197/#post-2112151