“Refundable” does not necessarily mean a full refund, no. On the other hand, if you were getting a full refund upon cancellation, then FareLock wouldn’t have made a ton of sense, as you could just refund the ticket if you didn’t need it.

To know what will happen if you need to request a refund, look for the “Cancellations” section in the fare rules, which you definitely should always review prior to purchase for any flight where you think a change or refund request is likely. UA does present them during the purchase process — look for “Fare Rules on the web. IIRC, it’s hidden behind “Legal Information” if purchasing through the app.