1. because set stage's width doesn't help, so use margin instead

2. adjust spacing when has different number of stages

osu.Game.Rulesets.Mania/UI/ManiaColumnStage.cs

@@ -155,6 +155,12 @@ namespace osu.Game.Rulesets.Mania.UI
             c.VisibleTimeRange.BindTo(VisibleTimeRange);
             topLevelContainer.Add(c.TopLevelContainer.CreateProxy());
             columns.Add(c);
+
+            Margin = new MarginPadding()
+            {
+                Left = columns.Count * HIT_TARGET_POSITION / 2,
+                Right = columns.Count * HIT_TARGET_POSITION / 2,
+            };
         }
 
         public void AddJudgement(Judgement judgement)

osu.Game.Rulesets.Mania/UI/ManiaPlayfield.cs

@@ -54,15 +54,18 @@ namespace osu.Game.Rulesets.Mania.UI
 
             Inverted.Value = true;
 
+            var stageSpacing = 300 / stages.Count();
+
             InternalChildren = new Drawable[]
             {
                 listColumnStages = new FillFlowContainer<ManiaColumnStage>
                 {
+                    Name="Stages",
                     Direction = FillDirection.Horizontal,
                     RelativeSizeAxes = Axes.Y,
                     Anchor = Anchor.Centre,
                     Origin = Anchor.Centre,
-                    Spacing = new Vector2(400),
+                    Spacing = new Vector2(stageSpacing),
                 }
             };