@neg177 It seems that the line items which are not mapped does not have any data in the source file, hence Anaplan engine is not allowing to map them manually. If you have values in those cells, it would either automatically map or allows manual mapping.
From your screenshot it would appear that all items that can be mapped in the target are allocated to a line item in the source. Unmapped items in the target will appear as blue in the box at the bottom right of the screen.
Ensure that all line items in the target which you want to import data into do not contain any formulas. Only empty line items will appear as mappable and will be marked in blue.