While it is not a condition that will stop you from being baptized, perhaps the below will help you understand why we believe in her perpetual virginity.
Scriptural Proof on the perpetual virginity of Mary:
“Then Joseph, being aroused from sleep, did as the angel of the Lord commanded him and took to him his wife, and did not know her till she had brought forth her firstborn Son. And he called His name JESUS.” Matthew 1:24-25
The use of the word “till” does not imply that Joseph had marital relations with Mary after the Savior’s birth. In the Bible, this word (sometimes translated “to”) is often used to express a situation that actually continues after the event mentioned (see Matt 28:20, Gen 8:7, Deut 34:6, 2 Sam 6:23.)
“While He was still talking to the multitudes, behold, His mother and brothers stood outside, seeking to speak with Him. Then one said to Him, “Look, Your mother and Your brothers are standing outside, seeking to speak with You.” But He answered and said to the one who told Him, “Who is My mother and who are My brothers?” And He stretched out His hand toward His disciples and said, “Here are My mother and My brothers! For whoever does the will of My Father in heaven is My brother and sister and mother.” Matthew 12:46-50
In Jewish usage, brother can indicate any number of relations. Abram called his nephew Lot “brother" (Gen 14:14); Boaz spoke of his cousin Elimelech as his “brother” (Ruth 4:3), and Joab called his cousin Amasa “brother.” (2 Sam 20:9) Christ himself had no blood brothers, for Mary was her only son. The brothers mentioned here are either his stepbrothers, sons of Joseph from a previous marriage, or cousins. If these were indeed Christ’s blood brothers, we would not see him committing her to John’s care when Christ was on the cross.
“Now there stood by the cross of Jesus His mother, and His mother’s sister, Mary the wife of Clopas, and Mary Magdalene. When Jesus therefore saw His mother, and the disciple whom He loved standing by, He said to His mother, “Woman, behold your son! Then He said to the disciple, “Behold your mother!” And from that hour that disciple took her to his own home.” John 19:25-27
If Mary had other children with Joseph, then assigning John to take care of Mary would not be a concern of Christ. (By this point in scripture Joseph has died. Women could not own property, and would be destitute if they did not have any children to look after them.) By assigning John as Mary’s caretaker, Christ affirms her perpetual virginity for all.
I hope this helps.