If your Self-Employment amount does not look correct to you, you will need to return to the T2125 - Statement of Business Activities and make any changes there.
Keep in mind that the amount that shows as Net Self-Employment Income in the summary is the amount after deducting any expenses and Capital Cost Allowance. If your Self-Employment was reported on a T4A slip, this figure will be lower than what is shown on the slip which is the Gross amount.