The entire 128x128 is completely inside of the map. Keep in mind that you can't precisely choose what blocks the map covers, so make the map THEN place the.
I was wondering what the command to get barrier blocks was I looked it up but the commands didn't work if you could tell me the command in the comments.
This Minecraft tutorial explains how to craft building blocks with screenshots and step-by-step instructions. You can craft different block items in Minecraft.
Across both Java and Bedrock editions, they can either be obtained by using the pick block control, or by using various commands, such as /give @s minecraft.