"At the end" means the specific point in time when something concludes or finishes, which is the intended meaning in this sentence.
"In the end" means eventually(വഴിയെ) or ultimately(ആത്യന്തികമായി) and is used to indicate the final outcome(അന്തിമഫലം) of a situation.
"In end" and "At end" are not idiomatic phrases. അവ ഈ സന്ദർഭത്തിൽ ഉദ്ദേശിച്ച അർത്ഥം നൽകുന്നില്ല.