unity – GameObjects gets small after spawning

As you can see here in the editor there is one size and in the game – another. I did try to oversize the part but it allways gets in one small size. I can’t understand why.
Here is the code to spawn:

using UnityEngine;
using System.Collections.Generic;

    /// <summary>
    /// Spawning parts, drop in partsPocket list
    /// </summary>
    public class SpawnerParts : MonoBehaviour
    {
        #region ========== Variables ========

        public GameObject selectedPuzzleVariant { get; set; }

        (SerializeField)
        (Tooltip("Place where to spawn puzzle at the begining of the game (pocket)"))
        Transform _spawnPos;

        List<Quaternion> _rotations = new List<Quaternion>();


        #endregion ========== Variables ========

        private void Start()
        {
            // Adding rotation variants
            _rotations.Add(Quaternion.Euler(0, 0, 0));
            _rotations.Add(Quaternion.Euler(0, 0, 90));
            _rotations.Add(Quaternion.Euler(0, 0, 180));
            _rotations.Add(Quaternion.Euler(0, 0, 270));            
        }

        #region ========== Methods ========

        /// <summary>
        /// Spawn parts in pocket
        /// </summary>
        /// <param name="positions"> Pocket's sockets positions</param>
        public void Spawn()
        {
            // Create & Hide puzzle
            GameObject parentPuzl = Instantiate(selectedPuzzleVariant, _spawnPos);

            foreach (var item in parentPuzl.GetComponentsInChildren<Part2D>())
            {
                item.SetParent(Main.Instance.MainCanvas.transform);
                item.RectTrans.anchoredPosition = _spawnPos.position;
                Main.Instance.partsPocket.Add(item);
            }

            Destroy(parentPuzl);
        }

        #endregion ========== Methods ========
    }

P.S. I can guess that the problem is that prefab’s parent is simple transform object without any RectTransform.

Screenshoot