I don't know wen you are flying, but there are plenty of VN flights SGN-PQC.during the day.
Currently there is one at 9:10 (not 9:30) and several after that (12:05, 13:35, ...).
You will have to clear immigration, collect your bags, move to the domestic terminal and recheck your bags. That will take time. It is certainly doable in 2 hours. But unclear if your QR flight is delayed by 30min, if your bags are slow to be delivered and without priority, if you need a visa on arrival...
But Vietnam domestic flights are so cheap! You can buy a one way ticket for USD20. SO I would not worry too much.