See, if I just amend your code then I doubt that you learn much.
There are so many things unconsidered in your code that it is even difficult to know where to start.
Do you had an ABAP training at all?
Do you know debugging?
Can you read the code?
Did you ever create a material master with its standard transaction?
Do you have a fundamental understanding of material masters?
I am certainly willing to help people over a hurdle, but you actually asked i shall send you the corrected code, and this is not my goal and is not the purpose of SCN either.
The bapi is pretty much structured according to the tables used to store material master information.
if you understand ABAP coding then you can see that almost anything is commented, which means will not be processed. What kind of material do you expect to create?
It might not be a bad approach to start small on one side, but you are actually fighting against a problem which you probably would not see if you tried to migrate a real material, which has all kind of plant views etc.
Back to your coding. You just cared about MARA the general data of a material. Goto MM01 and maintain the same values in the screen, then check the tables, MARA, MAKT, MARM (just to give you one more hint)
do all 3 tables have entries or only MARA?
If you see values in all three tables, then your coding just for MARA is to less to create a material. Would you share this opinion?