Welcome to FT!

Is the extra letter your middle initial, or the first letter of your middle name? Airline software will often append it to your first name on your travel documents. Everyone involved in screening, ticketing, etc., knows that his happens. I had a mistake once that included this as well as swapping my given and family names. At least one leg of that trip (MAA-SIN) was on SQ, perhaps also the next leg (SIN-NRT). It was not a problem.

If it's anything else, I still wouldn't worry. The U.S. security people allow up to three letters wrong, as long as what's left is sufficient to confirm that you're the person on your ID documents. Other countries tend to be at least as sensible as the U.S. in this regard, usually more so.

That said, I think this question is more about SQ than it is about Oceania. I've asked a moderator to move it to the SQ forum. Many more SQ experts, some of whom have never set foot anywhere in this region and would therefore have no reason to visit this forum, will see it there.