Samuel was lying down in the temple of the LORD, where the ArK OF GOD was located

[TonyChanYT]

Did Samuel sleep in the holy of holies at Shiloh?
No. Leviticus 16:

2 And the LORD said to Moses: "Tell your brother Aaron not to enter freely into the Most Holy Place behind the veil in front of the mercy seat on the ark, or else he will die, because I appear in the cloud above the mercy seat.

Where did Samuel sleep?
1 Samuel 3:

2 And at that time Eli, whose eyesight had grown so dim that he could not see, was lying in his room.

Eli was in his room.

3 Before the lamp of God had gone out, Samuel was lying down in the temple of the LORD, where the ark of God was located.

Samuel might not have his own room but somewhere near the ark of God before the veil.

4Then the LORD called to Samuel, and he answered, “Here I am.”
5 He ran to Eli and said, “Here I am, for you have called me.”

Samuel was within shouting distance of Eli.

“I did not call,” Eli replied. “Go back and lie down.”
So he went and lay down.

The night had passed.

15 Samuel lay down until morning and then opened the doors of the house of the Lord.

Eli had his own room inside the house of the Lord. Samuel was sleeping inside the house of the Lord within shouting distance of Eli, near the ark before the curtain.