Stout Overcarbed

I made a stout from a malt extract syrup kit and used 113g of sugar for 23 litres which should have achieved 2.1 units of CO2. It’s now 3 weeks since I bottled and I’ve opened two of them so far and they’ve been exceptionally fizzy and hard to pour without getting 50% head. I’ve not done a stout before, is this normal or do I need to age them for a lot longer?