I have to give a speech on this section of The Great Gatsby (Chapter 3, when Gatsby arrives).I'm analyzing a section when Gatsby comes in chapter 3...

It sounds like you have done a great job already! Yes,
Chapter III is of course our - and Nick's - first introduction to Jay Gatsby, and it is
key to realise how we have been prepared for his introduction by what others have said
about him and the rumours surrounding his rise to wealth and fame. You have done a great
job in identifying the "mask" that Gatsby puts on. Note too the use of unnatural phrases
like "old sport" in his dialogue and also the way that Nick
states:

Some
time before he introduced himself I'd got a strong impression that he was picking his
words with care.

It is also
important to note that just a couple of pages after this introduction Gatsby is
described as being on his own, isolated from his guests and the jazz age that he is so
eager to be a part of. It appears he doesn't "fit" in so many ways. And yet what
concerns me in your analysis is that it appears to focus too much on the negative
aspects of Gatsby. Let us also remember that in the same paragraph that your quote is
taken from, Nick tells us something very important about
Gatsby:

He
smiled understandingly - much more than understandingly. It was one of those rare smiles
with a quality of reassurance in it, that you may come across four or five times in
life. It faced - or seemed to face - the whole eternal world for an instant, and then
concentrated on you with an irresistible prejudice in your favour. It understood you
just so far as you wanted to be understood, believed in you as you would like to believe
in yourself, and assured you that it had precisely the impression of you, that, at your
best, you hoped to
convey.

There is certainly
more to Gatsby's character than just his "mask" of trying to fit in to the rich, wealthy
scene of his times, and with this description we are given an insight into his genuine
character that conveys to us just what an amazing kind of man Gatsby was - which of
course emphasises the tragedy of this story as Gatsby feels that he has to be something
he is not to gain the love of his life.