Yes you need closure of the ASD to prevent its complications. Best option would be either a device closure or robotic ASD closure.

Yes it is absolutely necessary to close it. If we don't close it earlier then it will lead to heart failure over a few years. As you can see the RA and RV are already dilated, so the damage to the heart is already in starting stage. The defect can be closed with a DEVICE or SURGERY; in your case you will require surgery as the defect is large, and it should be done on an urgent basis. Ideally these defects are found out and treated during early childhood stage itself, which has already crossed for you.