Since your witness cannot administer an oath, you have not made an affidavit. Signing something before a witness does not make it a sworn statement. The witness may be sworn by the notary, but since you were not under oath, you have not given an affidavit. Such a document has no evidentiary value and is worthless. The seal is only required on documents if necessary outside of Louisiana.
Notaries affix a mechanical seal or a stamp as a way of demonstrating the document is the original.
Louisiana's Civil Law System provides for much of our legal documentation to be passed by a Notary, who is a public official who has qualified for a commission authorizing those powers. Non-attorney notaries have to demonstrate a proficiency in legal matters within the scope of this broad power and authority by passing an examination administered by the courts. Licensed attorneys may be exempted from the exam. All notaries in Louisiana otherwise go through the same process to obtain a commission, and have the same powers. However, attorneys who are not commissioned as Notaries may not pass notarial acts.