How many is many? I don't know, but it would seem to be more than a few. Many will enter through the gate of destruction, and few will will enter through the gate of life.
It seems the majority of mankind will not be saved.
Are just a few being saved? Someone asked Jesus that very question, what did He say?
My understanding of these verses do NOT apply to the whole population of the world.
Jesus is not talking about the people of China, India, Africa, the Americas, etc, etc.
He is talking about the Jews - the chosen people of God through Abraham who by and large refuse to accept him as the long awaited Messiah.
Luke 13:22-30 gives a much clearer understanding of the warning about the narrow door and difficult is the way.
Luke 13:22 And he went on his way through cities and villages, teaching,
and journeying on unto Jerusalem.
23 And a certain one said to him, Lord, are the saved few? And he said unto them,
24 Strive to enter by the narrow door: for many, I say unto you, shall seek to enter, and shall not be able
25 when once the house-master is risen up, and hath shut to the door, and ye begin to stand without, and to knock at the door, saying, Lord, open to us; and he shall answer and say to you, I know you not whence ye are;
26 then shall ye begin to say,
We were eating in thy presence and drinking, and thou didst teach in our streets;
27 and he shall speak, saying to you, I know not whence ye are; depart from me, all workers of iniquity.
28 There shall be the weeping and the gnashing of the teeth,
when ye should see Abraham, and Isaac, and Jacob, and all the prophets, in the kingdom of *God, and
yourselves cast forth without.
29 And they shall come from east and west, and from north and south, and shall sit down in the kingdom of *God.
30 And lo, there are last who shall be first, and there are first who shall be last.
Read all the verses of condemnation that Jesus spoke against the Pharisees, the Sadducees, Scribes because they refused to repent and refused to accept Jesus as their Messiah sent from the Father.
He called them vipers, hypocrites, sepulchres full of dead men's bones, murderers of prophets, children of their father the devil, children of hell, blind guides, full of iniquity ...
and then there was 70AD - and read of the constant perils that Paul the apostle suffered from his own countrymen (who mostly rejected the gospel).
Luke 19:41 And when he drew near and saw the city [Jerusalem], he wept over it,
Luk 19:42 saying, “Would that you, even you, had known on this day the things that make for peace! But now they are hidden from your eyes.
Luk 19:43 For the days will come upon you, when your enemies will set up a barricade around you and surround you and hem you in on every side
Luk 19:44 and tear you down to the ground, you and your children within you. And they will not leave one stone upon another in you,
because you did not know the time of your visitation.”