If the answer is just ? "twbydy" = two by two = square, "am" = morning = A.M., "by 3" = ×3? Not fitting.

(since it says "piece" in the prompt): "TRI" or "TRIO" ? But length 3 → "TRI" .

Given typical puzzle answer lengths, is a clue for "AM" with something? No.

Given typical cryptic answers: I’ll go with (from tri = three, "by 3" = times three, "am" = "I am" = "I" in Latin? No).

But: if this is a from a larger set, and the answer length is given as 3 letters, then "by 3" means the word is 3 letters long, and the preceding text gives the wordplay.

(Roman numeral for 3, "piece" as in a piece of a set).