To support what Lilmod said that am yisroel means all of am yisroel, I would suggest that since Hashem is total Emes, then anything He says has to be pure, complete truth. If “Ahavti Eschem” meant am yisroel as a whole but not every individual, I think that the statement would not be 100% true. But that cannot be, since Hashem is 100% emes. besides, we say that even a sinner is part of am yisroel (except maybe a total kofer), so he would be included in the eschem.
That said, I too am a bit bothered by using “Hashem loves you” as a slogan because it reminds me of other versions of this statement put out by other religions, but keep in mind, that the statement is not meant to stand alone and mean that because of that we are absolved of all our sins and everything is great, but rather Hashem loving us means that we are obligated to prove that love and live by His Torah.