In the final level, you have to make columns of 4 happy square people. If you get too far past your highest happy column, a laser will blast the furthest-right square person and remove them. The laser priorities right to left, top to bottom.
All you really need to do is let any seals you place get blasted. Making happy columns without using seals is not that difficult. If you can, keep to a pattern like this:
(G = Girl, R = Robot, N = Nerd)