he didn't. He told them to repent. Then told those who repented to be baptized.
Acts 2:38
(ASV) And Peter said unto them,
Repent ye, and be baptized every one of you in the name of Jesus Christ
unto the remission of your sins; and ye shall receive the gift of the Holy Spirit.
(BBE) And Peter said,
Let your hearts be changed, every one of you, and have baptism in the name of Jesus Christ,
for the forgiveness of your sins; and you will have the Holy Spirit given to you.
(CEV) Peter said,
"Turn back to God! Be baptized in the name of Jesus Christ, so that your sins will be forgiven. Then you will be given the Holy Spirit.
(ISV) Peter answered them, "
Every one of you must repent and be baptized in the name of Jesus the Messiah for
the forgiveness of your sins. Then you will receive the Holy Spirit as a gift.
(KJV) Then Peter said unto them,
Repent, and be baptized every one of you in the name of Jesus Christ
for the remission of sins, and ye shall receive the gift of the Holy Ghost.
(LITV) And Peter said to them,
Repent and be baptized, each of you on the name of Jesus Christ
to remission of sins. And you will receive the gift of the Holy Spirit.
(MKJV) Then Peter said to them,
Repent and be baptized, every one of you, in the name of Jesus Christ
to remission of sins, and you shall receive the gift of the Holy Spirit.
(Webster) Then Peter said to them,
Repent, and be baptized every one of you in the name of Jesus Christ,
for the remission of sins, and ye shall receive the gift of the Holy Spirit.
(WNT)
"Repent," replied Peter, "and be baptized, every one of you, in the name of Jesus Christ,
with a view to the remission of your sins, and you shall receive the gift of the Holy Spirit.
(YLT) and Peter said unto them,
`Reform, and be baptized each of you on the name of Jesus Christ,
to remission of sins, and ye shall receive the gift of the Holy Spirit,
Now as I understand English and I should as I taught English, it says that if we want remission of our sins we have to repent and be baptised.
There is no indication here, that Peter went round to find out who had repented. He was addressing the crowd and told them all regardless of whether they had repented or not that if they wanted remission of sins, they had to repent and be baptised.
If you are unable to understand these basics of English, your interpretation of scripture is going to be whatever you make up at any given time.