I did a test. We can use this.chart1.Size = new Size(300, 100);
to modify the size of the chart.
But I checked your code, you wrote this code twice:
this.chart1.Size = new System.Drawing.Size(300, 100);
this.chart1.TabIndex = 0;
this.chart1.Text = "chart1";
this.chart1.Size = new System.Drawing.Size(353, 428);
Is the second one redundant? Did you only modify the first one?
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