See there are two parameter in the job and you are passing sysdate and the 'NEXT_DAY(TRUNC(SYSDATE),''SUNDAY'')+3/24');

so in case of first parameter which is sysdate it will fire as soon as you run that job and the second parameter is the due date parameter so do one thing put this string(NEXT_DAY(TRUNC(SYSDATE),''SUNDAY'')+3/24) in both the parameter

begin
DBMS_JOB.SUBMIT(:jobno, 'CALL_WEEKLY;',
NEXT_DAY(TRUNC(SYSDATE),''SUNDAY'')+3/24,
'NEXT_DAY(TRUNC(SYSDATE),''SUNDAY'')+3/24');
end;

Hope this will work

Shailendra