You need to "Edit" each T5008 slip from the T5008 Summary page to add your Box 20 amounts. (You can also choose to add up all your T5008 slips and enter as one entry on the T5008 slip page).
When you are looking at the T5008 Summary page, what you are seeing are the amounts you entered in Box 21 of the T5008 slip only. The actual capital gain/loss is not seen on this page.
After completing all your entries, if you have a Capital Gain, you will see it on Line 127 of the Detailed Tax Summary. Capital Losses are not seen on the current year's tax return.
You can also see these entries after you pay for your return (even the Free version must go through the payment process) on the PDF view of the T1 General.