Testing results

That meal is very high in fats as well as carbs. The fats are probably slowing down the bg rise, and might do for several hours.
Some users report pizza spiking them the next day!
Your one test is probably missing the spike which might be prolonged more than straight up and down.
Consider getting a libre which will monitor you more often. The first one is free and lasts 2 weeks. Subsequent ones cost about about £50

I don’t see how you can assess how much the rise is if you didn’t take a reading before your meal. However I do agree with @MrsA2 your meal contains a lot of fat so might delay a further rise.

The most important time to test is just before you take your first mouthful, be it breakfast, lunch or dinner. Then compare that first reading with the result two hours later.

The second reading should be no more than 2 mmols/l above the first one and no higher than 8 mmols/l. By reducing the carbohydrates in your meals, you can bring those results down to a healthy range.

If I’d eaten that I’m sure my BG would be in the 20s

As @LivingLightly and others have said test just before you eat and 2 hours after. Try and cut carbs as best you can to stop complications in the long run