It could have been a lot worse.
I believe that Dyer had a couple of armoured cars, with machine guns, with him. They could not get into the park, due to it's gateway being too narrow.
Sir Michael Francis O'Dwyer, GCIE KCSI was Lieutenant Governor of the Punjab in 1919, and had endorsed Reginald Dyers actions.
In March 1940 in London Udham Singh, a Sikh who had survived Amritsar, shot dead Micky O'Dwyer. He used a service revolver that he bought from a soldier in a pub.
After going on hunger strike Udham Singh was hanged. His body was returned to India in 1974:
https://www.nytimes.com/1974/08/05/a...r-tied-to.html