As there is no way to add another line to this section of the Schedule 3 in TurboTax, you will have to add a couple of your transactions together.

Often times a taxpayer will enter a "total sum" on the Schedule 3 in regards to multiple Capital Gain transactions. It's ok to do it this way, just be sure you have your documents available if CRA requests to see them. 

The actual Schedule 3 form from CRA only has one line, completing that and paper filing your return with that attached is not really an option either.