OK, I made several mistakes.
Apparently I have created a user the first time when I invoked ./install.sh.
But then I encountered a problem with network (us.ncr.io is blocked), I cannot pull sentry-relay image so sentry service is incomplete.
After I resolved the network issue by setting a proxy for docker, I ran install.sh again. But this time the script will skip user creation.
I then totally forgot the fact that I have already created a user yesterday when I tried the first time.
with docker-compose run --rm web createuser I created a new user and I can now login into sentry.