My 2 week old newborn feels warm to touch and appears too hot (room temp is 27 degrees) during these hot summer nights. I don't have aircon so I dress him to the room temperature - 1 tog sleeping bag & nappy. His body temperature (armpit method) shows he is 36.1 which is confusing as it's on the lower end of the normal temperature range. Is this normal despite him feeling hot?

Babies should feel “snuggly warm” on tummy/back. If temp is 36.1 under armpit that is certainly a “comfortable” temperature for baby. (The armpit method will generally be lower level of normal.)
Sounds like clothing amount is reasonable on those hot nights.
Are you wrapping/swaddling him as well as the sleeping bag, or is he in a “swaddle” bag - arms in? - sleeping bag has arms out
Does he have any extra bedding?

It is difficult to be specific as to what exact clothing/bedding a baby uses, but you are correct in dressing him according to the room temperature. Have a read of the article linked below.
https://rednose.org.au/article/what-is-a-safe-room-temperature-for-sleeping-baby