Hey Aleks555! Based on image , burying that stretched stem was definitely the right move to help stabilize your plant and give it a chance to grow a stronger root base from that buried section. Since you mentioned everything seemed fine at first but it's now an "unfortunate issue," watch out for any signs of damping off or stem rot if the soil stays too wet against the stalk. To stop any further stretching, make sure your light intensity is dialed in and maybe add a small fan to create a light breeze, which helps the stem thicken up and get sturdy enough to support those beautiful leaves!
Happy Growing Growmie🌱