You are overlaying the first three bytes of the record with the sequence number. How do you know that's what the OP wanted? Given that the OP said "insert", I'd assume that the OP doesn't want to overlay the data. But it's not clear exactly what the OP does want. That's why I asked for an example of input and output to clarify what's wanted.
Please don't take wild guesses without explaining your assumptions as it just confuses people.