Accidentally saying "El Melekh Neeman" when in a tzibbur

Question

There is a very widespread custom of commencing one's recitation of the Shema with the three-word phrase, אל מלך נאמן, when davening alone, and of having the shaliach tzibbur repeat the last two words of the Shema, plus the first word of Emet veYatziv (= ד אלהיכם אמת) when davening with others (see Orach Chayim 61:3). The reason for this is that the Shema has exactly 245 words, and by adding an additional three we bring that number up to 248, which is the number of positive mitzvot (and human limbs, etc).

(See also Siddur Vilna, pp. 83–84 and 88)

My question: if somebody regularly davens alone, they might get into the habit of adding three words at the beginning, as described. In the event that s/he then finds themselves davening with others, but accidentally says אל מלך נאמן before commencing, what should s/he do?

• Should s/he continue as usual and not worry about it, since it's only a custom and does not affect the status of the Shema?
• Should s/he pause, then recommence without that additional passage?
• Should s/he continue as usual, but not wait for the shaliach tzibbur and just continue straight into Emet veYatziv in order that the number of words recited in the Shema is 248 and not (technically) 251?
• Or is there something else that should be done?

Answer 1

The original minhag ashkenaz was to say kel melech neeman in all situations, when davening with a minyan and by oneself. (found in Rokeach, Agur, Tur, Siddur Shlomo Worms Maharik and other Ashkenazi Rishonim and early achronim) Some Achronim, including the Maharshal (tshuvah 64) and elaborated by his student in Mateh Moshe 1-88, yosif ometz-17) began to question saying kel melech neeman. One of the issues mentioned it is an interruption between the bracha and the shema (maharshal concludes never to say it) The Rema in siman 61 sif 3 concludes that betzibur one should say Amen in place of (and have in mind) the words kel melech neeman (roshei tevos of kel melech ne'eman are aleph mem nun=amen) and for the chazzan to repeat out loud: hashem elokechem emes at the end of shema. (minhag Poland similar to sefard, as opposed to western ashkenaz that only repeated the word emes). (Some later authorities have suggested that even answering amen is an interruption, resulting in some answering amen while others refraining)

However, when saying shema biyechidus many [rema and in darkei moshe] have the custom to continue saying kel melech ne'eman to complete sum of 248 (since one cannot replace it with Amen and there is no chazzan to repeat hashem elokechem emes).

If one accidentally said kel melech neeman (as was the original minhag ashkenaz supported by many rishonim) when davening with a tzibur, there is certainly no reason to not wait for the chazzan at the end of shema. One may proceed as usual and is relying on the original minhag ashkenaz, at most one doesn't have to have in mind when hearing hashem elokechem emes repeated from the shliach tzibur to add to 248 but one should certainly wait for the shliach tzibur. There is no issue with hearing too many words. Even according to the Rema, one answers amen before shema and hears hashem elokechem emes at the end and then says the 15 vavs which would add up to more than 248 and isn't concerned by this.

[Rema and mechaber give another way for someone to arrive at 248 words without saying kel melech ne'eman when saying emes vyatziv there are 15 instances of the letter vav. When added up equals hashems name 3 times, thereby making up the missing three letters (rema gives an additional explanation). Note; there is no talmudic source for having 248 words in shema. It is implied by tanchuma kedoshim that there are 248 words but there is no mention of how that is arrived at. Zohar says including hashem elokechem emes adds to 248(some interpret ani hashem elokechem (not emes). Some rishonim such as rokeach mention adding kel melech ne'eman before shema to arrive at 248. It is certainly not meakev.]