Utilitário para criação de carrosséis na Unity

carrousel.cs

using System.Collections;
using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

[RequireComponent (typeof (ScrollRect))]
public class Carrousel : MonoBehaviour, IBeginDragHandler, IEndDragHandler {

    [SerializeField]
    [Range (0.05f, 1f)]
    private float lerpAmount = 0.1f;

    private ScrollRect scrollRect { get { return GetComponent<ScrollRect> (); } }
    private HorizontalLayoutGroup content { get { return scrollRect.content.GetComponent<HorizontalLayoutGroup> (); } }
    private RectTransform contentRectTransform { get { return scrollRect.content.GetComponent<RectTransform> (); } }
    private List<RectTransform> contentObjects { get { return content.transform.Cast<RectTransform> ().ToList (); } }
    private float cardSize { get { return contentObjects[0].rect.width; } }
    private float cardQuantity { get { return contentObjects.Count; } }

    public int CurrentCardIndex = 0;
    private bool isDrag = false;
    private void OnEnable () {
        RectTransform viewport = scrollRect.viewport;

        Debug.Log (viewport.rect.width);
        int padding = (int) (viewport.rect.width - cardSize) / 2;
        content.padding.left = content.padding.right = (int) (scrollRect.GetComponent<RectTransform> ().rect.width - cardSize) / 2;
    }

    public void OnBeginDrag (PointerEventData e) => isDrag = true;

    public void OnEndDrag (PointerEventData e) => isDrag = false;

    public float RoundValue (float current, float multiplier) {
        float rest = current % multiplier;

        float minimum = current - rest;
        float maximum = minimum + multiplier;

        return rest > multiplier / 2 ? maximum : minimum;
    }

    float objetiveValue = -1;
    public void AddIndexToCarrousel (int index) {
        CurrentCardIndex = Mathf.Clamp (CurrentCardIndex + index, 0, (int) cardQuantity - 1);
        objetiveValue = CurrentCardIndex * (1 / (cardQuantity - 1));
    }

    private void Update () {
        if (!isDrag) {
            if (objetiveValue != -1) {
                scrollRect.horizontalScrollbar.value = Mathf.Lerp (
                    scrollRect.horizontalScrollbar.value,
                    CurrentCardIndex * (1 / (cardQuantity - 1)),
                    0.1f);

                if (Mathf.Abs (objetiveValue - scrollRect.horizontalScrollbar.value) < 0.01f)
                    objetiveValue = -1;
                return;
            }

            int padding = content.padding.left;

            float carrouselSize = cardSize * cardQuantity;

            float cardSizeInScroll = 1f / (cardQuantity - 1);
            float paddingInScroll = padding / (contentRectTransform.sizeDelta.x);
            float roundedValue = Mathf.Clamp (RoundValue (scrollRect.horizontalScrollbar.value, cardSizeInScroll), 0f, 1f);

            scrollRect.horizontalScrollbar.value = Mathf.Lerp (scrollRect.horizontalScrollbar.value, roundedValue, lerpAmount);
        }
    }
}

Use da seguinte maneira:

Código dentro do objeto na seta vermelha

Adicione o componente "Horizontal Layout Group" e "Content Size Fitter", arrange-os desta maneira:

Pronto, tudo feito, aproveite e mexa de acordo com suas preferências.