We have all made some type of mistake like this.
After a while, you can either order new bushings with each bunch of kits OR order kits that you already have the bushings.
Personally, when I try a new pen kit I try to use the bushings I have or order a complete bushing kit with the drill bits that are needed. And I have even doubled up on drill bits at times.
They don't go to waste lucky for us.
Enjoy the hobby and fun. Laughing at yourself is part of the fun.
It's not "Having what you want"......it is "Wanting what you have".
"Don't go riding on that long black train."