I changed mine a couple of weeks ago and thought for sure there were 4, one on each side of both banjos. But I just took a look. There is one on each side of the banjo at the lever for sure. If there are only 3, at the caliper the upper one (bolt head to banjo) is definitely there
The one on the bottom of the caliper end banjo (banjo to caliper) is not obvious so that would be the one to leave out, if you only have 3.