I believe the word is "in," not "there." If you'll notice, the third time the chorus is sang with little music, you can hear the words clearly, and the word after "kept" clearly does not end with an "r" sound. "Every little secret that I kept IN, locked inside my heart..." Some artists will "repeat" a word (although "in" and "inside" are technically not the same word, but you get my point) like that within the same verse.