SQL Problem Cant Create A Procedure

create proc sp_fillrowintable
(
    @tablename nvarchar(50),
    @colvalue    nvarchar(100),
    @id int

)
as

declare @colname nvarchar(30)
declare @colid nvarchar(30)
--declare @tablename nvarchar(50)

--set @tablename = @table

select @colid = column_name from information_schema.columns where table_name = @tablename and data_type ='int'
select @colname = column_name from information_schema.columns where table_name = @tablename and data_type ='varchar'

if(@id = 0)
begin
    select @id = max(@colid) from @tablename
    Insert into @tablename values (@id,@colvalue)
end
else
begin
    update @tablename set @colname = @colvalue where @colid = @id
end

 
getting errors at my side while executing this script
 
Msg 1087, Level 15, State 2, Procedure sp_fillrowintable, Line 21
Must declare the table variable "@tablename".
Msg 1087, Level 15, State 2, Procedure sp_fillrowintable, Line 22
Must declare the table variable "@tablename".
Msg 1087, Level 15, State 2, Procedure sp_fillrowintable, Line 26
Must declare the table variable "@tablename".
Msg 156, Level 15, State 1, Procedure sp_fillrowintable, Line 26
Incorrect syntax near the keyword 'where'.

 
help me out
 I want to insert and update rows for various table having only 2 columns in each table.
want to insert and update rows in these tables.
 please tell me is it possible to do this through stored procedure or i have to do inline query in .net