Russian's use of gender means your translation isn't correct. In "Is this your spoon" "this" is acting as the subject by itself and will be always translated as "это" no matter the gender. "Эта" in the question is specifically modifying the spoon ("this spoon"). In English the correct answer and yours have slightly different meanings but use the same words, which can make it confusing
Yes, I thought I wrote "Is that spoon yours?" but seeing that someone else had commented on it and Janisa has added it, I realized I might have turned it around. I do understand the nuances in English. So in Russian, "Is that your spoon?" would simply be "Это твоя ложка?"