Dear Muhammad,
I do not think you can restrict addition of same component multiple times inside a BOM.
If large number of components are causing problems, you can use phantom assemblies to simplify the BOM. Phantom assemblies are logical grouping of components and you can have multiple level of phantom assemblies.
Moreover you might seek for an LSMW or BDC to create the BOM from an excel or tab-delimited file so that such errors do not take place.
Best Regards,
Rajen