There are way more volcanoes under the ocean than on land. I think the ratio in your post is probably good.
But the CO2 that under-sea volcanoes emit do not make it into the atmosphere except through the ocean emission numbers.
Ocean CO2 emissions 90.0 billion tonnes (Carbon)
Ocean CO2 absorption 92.0 billion tonnes
Man-made CO2 emissions 7.0 bilion tonnes
Some have noted there are differences in the numbers quoted. Usually the data is quoted in “Tonnes of Carbon”. If it is quoted in “Tonnes of CO2”, it is about 4 times higher since now you have a carbon atom and two oxygen atoms in the atomic weight. You have to be careful with what they are measuring.
Usually just the Carbon numbers are used and the Carbon cycle is measured since oceans and plants convert CO2 into different Carbon molecules when they absorb CO2 but it gets converted back into CO2 when it is emitted. So you need to look at it as a complete Carbon cycle and using just the Carbon weights is a better way of lloking at the whole system.