Davening Mincha then Maariv back to back with a little Torah in between. Kriat Shema must be said after Tzais Hakochavim however when Davening Maariv right after Mincha the sky still has some blue with no stars in sight. When I go home after Maariv am I supposed to wait until Tzais Hakochavim and say Kriat Shema on my own or am I covered for the rest of the night during Maariv?
It seems from your description that you Daven Maariv before Tzeit Hakochavim (nightfall - when stars become visible at night). In this case you are definitely obligated to repeat Kriat Shema without its Brachot after Tzeit Hakochavim. The time of Kriat Shema Shel Arvit is at night after Tzeit Hakochavim, as is learnt from what it says “Uveshachbecha” (and when you lie down) and before night it is not the time of lying down. The length of time of twilight, which is the time period between sunset and nightfall, and also the time of nightfall differ from country to country, and place to place, so you should find out exactly when is Theit Hakochavim in your place in order to say Kriat Shema on time. There are various customs in Israel regarding the time of nightfall. Some have the custom of about 15-20 minutes after sunset, some wait until about 40 minutes after sunset, others are stringent and wait until about 72 minutes after sunset. Rabbi Moshe Feinstein describes at length in Igrot Moshe Orach Chaim 4, 62, how one should act regarding times in America. [שו"ע או"ח סימן רלה סעיף א ובמ"ב, אשי ישראל פרק כח סעיפים ט-יב, שש"כ פרק כ הערה קפה, הליכות שלמה פרק יג סעיף ט ושם בארחות הלכה 28 ו32 ].