The most distinct early memory I have is when I was in Hawaii with my dad. I believe was four years old. We were at a resort, relaxing in a hot tub with my dad's friends. Although hot tubs seem shallow to adults, it seemed very deep to me at the time. I remember being held by my father in the hot tub when suddenly I slipped from his arms and fell under the water. I was terrified and thought that I was drowning! I'm sure tht I was only submerged for a few seconds, but at the time, it felt as if I was under water for a while; it was very scary.
Is that "drowning" toddler still me? Yes, I still feel like the same person; I feel continuity with that little girl. However, I am a more experienced version of that girl. I know now that I shouldn't have been frightened because my dad was there to catch me. This memory, however, is the first personal instance that I can relate to and claim to have continuity with.
I can relate to your earliest memory. I think experiences that cause distress must be easier to remember. My earliest memory was also a rather traumatic experience. There must be some connection between experiences that cause physical or emotional pain and the memories you remember the most clearly. The profound distress you experienced at this young age probably contributed to why it's your most clear memory from early age.
