Question: If the transgression of Adam and Eve was actually a blessing for them, then why did they feel guilty and afraid when God approached them in the Garden of Eden after they committed their transgression?

Partaking of the fruit gave them knowledge of good and evil, and so their moral awareness made them feel guilty for doing wrong

Adam and Eve were guilty and afraid because they knew they had violated a commandment of God, and had been told the consequences of doing so. They had also not been taught the gospel or about the Plan of Salvation, and so did not know that the atonement of Christ could free them from the effects of their acts.
Furthermore, partaking of the fruit gave them knowledge of good and evil, and so their moral awareness made them feel guilty for doing wrong.
When Adam and Eve learned of the plan of salvation and repented, they did rejoice. Upon learning of Christ,

...the Holy Ghost fell upon Adam, which beareth record of the Father and the Son, saying: I am the Only Begotten of the Father from the beginning, henceforth and forever, that as thou hast fallen thou mayest be redeemed, and all mankind, even as many as will. And in that day Adam blessed God and was filled, and began to prophesy concerning all the families of the earth, saying: Blessed be the name of God, for because of my transgression my eyes are opened, and in this life I shall have joy, and again in the flesh I shall see God. And Eve, his wife, heard all these things and was glad, saying: Were it not for our transgression we never should have had seed, and never should have known good and evil, and the joy of our redemption, and the eternal life which God giveth unto all the obedient. (Moses 5꞉9-11

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Notes

Question: If the transgression of Adam and Eve was actually a blessing for them, then why did they feel guilty and afraid when God approached them in the Garden of Eden after they committed their transgression?