What is the proper procedure for the evening Shema when one is also ready to recite Shema al HaMita?

Question

If a person has already davened maariv before the time for shema and needs to say it now at night, and also needs to say Kriat Shema al HaMita before retiring, what is the proper way he/she should say the evening Shema if they want to fullfill his/her obligation? There are two ways I could think of, however, if there are mekorot that mention other ways then even better.

The two options I had in mind were:

A. Say the entire Shema in full and then say Shema al HaMita

B. Say Kriat Shema al HaMita and where you say the first paragraph of Shema, instead insert the full 3 paragraphs

Are either of these methods the correct procedure?

Answer 1

Halachipedia says:

If one didn’t repeat Shema after Tzet HaKochavim one must say all three paragraphs and should have the proper intent to fulfill one’s obligation.[5]

Reference 5 is to the Mishna Berurah 239 (1).

The SO O Ch starts

קורא על מטתו פרשה ראשונה של שמע ומברך המפיל חבלי שינה על עיני וכו':

On the words פרשה ראשונה, Mishna Berurah says:

( פרשה ראשונה - ואם התפלל ערבית מבעוד יום צריך לקרות כל הפרשיות ויכוין לצאת בהן המ"ע של ק"ש וגם המצוה של זכירת יציאת מצרים. וטוב לומר תמיד כל ק"ש שהיא רמ"ח תיבות [בצירוף אל מלך נאמן] לשמור רמ"ח אבריו:

If he prayed Maariv early, he needs to read all three parshiyos and to have intention to do the positive mitzva of reading Shema and the mitzva of remembering the Exodus. It's best always to say all three paragraphs with אל מלך נאמן to guard the 248 limbs.

From here we see that it is acceptable to say Kriat Shema al HaMita and where you say the first paragraph of Shema, instead insert the full 3 paragraphs.

O Ch 235 says

לכתחלה צריך לקרות ק"ש מיד בצאת הככבים וזמנה עד חצי הלילה ואם עבר ואיחר וקרא עד שלא עלה עמוד השחר יצא י"ח:

Ideally, it is necessary to read Shema as soon as stars are visible and the time extends until midnight ; if he delays until amud hashachar, he has still done the mitzva.

So, if one davenned Maariv early, the best thing to do is to read Shema as soon as stars are visible. Then one can say Kriat Shema al HaMita in the normal way, preferably with all three parshiyos.

But if one did not do this then as stated above, it is acceptable to say Kriat Shema al HaMita and where you would have said the first paragraph of Shema, instead insert the full 3 paragraphs with the proper intentions.