Went to see an endocrinologist about my graves' disease, and he thinks I should have a thyroidectomy, are there any risks I should know?

Various opinions. In your age group, the most recommended treatment for graves disease is taking anti-thyroid drugs (methimazole). If this does not result in remission of your disease, most endocrinologists would recommend treatment with radioactive iodine. Surgery for graves disease is not commonly done in the us, though is more common in europe and the far east.
Few rare complicatio. Because you are 20 yr old medications will harm if you are going to have a baby, same reason for not to give rai. Besides usual surgical & anaesthetic complications , specific to this surgery injury to superior laryngeal nerve causes loss of high pitch voice inferior causes hoarseness , both are extremely rare.Parathyroid injury also rare.