So did the opium wars have more deaths than WW1?

Not even close. Estimates of WW1 deaths vary from about 15-20 million. The total casualties for the opium wars (both of them combined) were well under 100,000, and the number of deaths even lower. The total Opium War death toll was less than 1% of the WW1 death toll.

The much deadlier war between China and the West was still to come: the Boxer Rebellion. Reliable numbers for deaths are lacking, but plausible estimates are about 100,000. Even adding the Boxer Rebellion to the opium wars leaves the death toll under 1% of WW1.

The major Chinese war of the Opium War period was not either of the Opium Wars - these were little sideshows in comparison. The main war was the Taiping Rebellion, which was not only the biggest war in China of that period, but a good candidate for the biggest war anywhere in the world in the 19th century. It affected most provinces in China, and lasted well over a decade. Most reasonable estimates of the death toll are about 20-30 million, greater than the WW1 death toll.

It's possible that the Taiping Rebellion has been conflated with the Opium Wars, either by your teacher or your memory.