Execute Immediate In Trigger

I am trying to use execute immediate in a trigger. See the below example

create table test_tbl(col1 number,col2 varchar2(10), col3 date);
create table test_tbl_log as select * from test_tbl where 1 = 2;

create or replace trigger test_trig
after insert or update or delete on test_tbl
for each row
declare
v_str varchar2(4000);
[code].......

insert into test_tbl values(3,'test',sysdate);

I got the Error : -1008->ORA-01008: not all variables bound

In the execute immediate statement if I change the v_using_str variable to :new.col1,:new.col2,:new.col3 trigger is running fine. But here I have to create trigger on all the tables in my schema and I dont want to list all the column names for each table manually and I am using a for loop to build the v_using_str string in my original code.