It is possible that your disinfectants are bacteriostatic rather than bacteriocidic, that is, they only inhibit bacterial growth. In this case you may not see (any visible) effect after the bacteria have already grown. It may also take a while for the dead bacterial colonies to disappear from your plate – you could check their viability for example by making a replicate plate from your test plate, or by inoculating some of the bacteria close to the disc to another agar plate, and see if they grow.

In case your disinfectants do not kill bacteria but are bacteriostatic instead, you can find some comfort from the fact that the people you said did this online might’ve used bacteriostatic substances as well, and mistakenly think they were killing the bacteria, whilst they actually only prevented their growth – because the effect looks the same when you put the discs on the agar right after inoculation 😉

After all, as far as I know most of the common household disinfectants are fairly weak, and many bacteria tolerate them, or easily develop resistance. What sort of bacteria and disinfectants you are using?

What you read on the web is the correct way to test for inhibition of growth, and what you did was wrong, in spite of what your teacher told you.
Bacteriostatic or bactericidic do not change the result: once the colonies have grown in a lawn (to confluence), you won’t see a difference if they die (they usually do not melt away, the walls are still there) or if they simply stop growing… or if they are perfectly healthy. In fact the disc diffusion method do not alllow to make the difference between bacteriostatic and bactericidic substances. The only thing it allows you to do in such setting is to compare the relative efficiency of the same antibiotic relatively to different bacteria. In fact results between different species of bacteria should be handled with precautions, but that is another story. So if I were you, I would simply restart the experiment if possible, and put the disc on freshly inoculated plates.