I recently fed my lawn with a soluble lawn feed that said to put half a
sachet in a watering can with 2 gallons of water and spread over 20 sq
meters. Things did not go perfectly.

First off, this seems to be a very light covering, so it was difficult
to move quickly enough to avoid exhausting the 2 gallons well before
covering 20 sq meters. I had hoped to go over the area twice, in
perpendicular directions, to get even coverage, but that just wouldn't
work. I only managed to go in one direction.

The end result was that I have a fairly striped lawn now of alternating
yellowish and lush greenish lawn. My guess is that the yellowish got
very little feed (it looks pretty much like it did before the feed,
though admittedly it's hard to know). But could it have gotten too much
and be slightly burned? How can I tell the difference?

I was thinking of mixing a more dilute batch and going back over the
yellowish stripes.

What should I do to avoid this problem next time? More dilute? Invest
in a spray attachment for the hose? Switch to a dry feed like Growmore?