Your criteria for determining that the "dry" gum had no effect was to swallow a 4 mg dose and note that you felt no effects. You reasoned you would notice the effects because it made you dizzy last time you took that dose - but then you also noted that you didn't eat dinner, which could have also caused the effect, confounding your judgement.

I don't recall eating dinner before the test either, so that wouldn't be a confound.

However, you also noted that your guesses as to whether or not you had the placebo were worse than chance. This means that you aught to assign low confidence to your ability to predict whether or not you are under the influence of nicotine.

You're not comparing like with like here: 4mg is different from a 1mg dose. It's 400% larger, to be specific. If I took 800mg of modafinil rather than 200mg, I think I'd notice that...

It is possible that the reason you were having trouble guessing because you were getting nicotine both in the "dry" and regular gum, albeit probably at different doses. Do you have a good reason to be confident that the nicotine would evaporate quickly from gum, other than knowing that it evaporates quickly and not subjectively feeling any effects from a dry 4mg dose?

There's no reason that the nicotine would not evaporate. There was a lot of surface area (2 cut sides in addition to the substantial permeability of the gum itself), and I kept it out for 3 or 4 weeks, while all the sources I found spoke of substantial evaporation within minutes or hours and patches being useless after around a day - so I was giving myself a safety factor of >20x precisely to avoid this sort of issue.

Given the precautions I took, I think it's much more likely that the placebofying succeeded and my poor predictions were due to other factors: eg. tolerating to the point where 1mg did not produce significant effects (I hope not, since this would imply that my spacing out of gum use has failed and also that my experiment was an effort in measuring a null effect), the use of nicotine each day without any spacing out (see the writeup, I did this to avoid wasting gum since it was use-it-or-lose-it), or just another demonstration of how significant placebo effects can be (wouldn't be the first time!).