Hi Sine ,
Did you used the "Auto Field Mapping" ?
I prepare exemple based on your data in the screenshots
use the option "import projects" then select the file "LSMW_DEV_BOM_CREATE.txt"
and use the button
in the next screen to complete import - now search new project in the name BOM_CREATE which I created based on your screen shots where all the fileds in the source are mapped
When you will find the BOM _CREATE project goto tp th 5'th LSMW step "Maintain Field Mapping and Conversion Rules"
and check the mapping done
Please update
Hopes this help!
Regards,
Ziv