I was comfortable right off the bat too. Of course, I always loved water, swimming, being in the ocean, etc. I was a lifeguard in my teen years too. So I had a head start. It gets easier and more relaxing for most people over time. Like another poster said, don't worry about it. Hey, improving is always good, right!
I remember my first open water dives (two on the first day)... On the very first dive I was kneeing in line with my fellow students there in the sand at about 30 feet. The swaying back and forth in the surge was kind of relaxing. There wasn't much to look at while waiting for my skills to be tested, but then when I focused my eyes right in front of me I saw krill for the first time! (I was probably cross-eyed in retrospect). It was so relaxing...and peaceful... I kind of felt at home in a way... sitting there on the ocean floor with my eyes crossed.
Then it was my turn for skills, I went though the whole rig-a-ma-roo and then the instructor got to me and signaled to me to show how much air I had left, I looked at my gauge and signaled back to him. He asked me again and I signaled again. Then took the gauge and looked himself then looked at me. Then we all swam off.
When we got back to the shore, he asked me if I was holding my breath (I wasn't). I don't think he believed me and I think he kept a closer watch on me the second dive. On that dive we calculated SAC rates.
At one point on that second dive, the taste of salt in my mouth (from the swim out and from doing the out of air drills) was starting to gag me though and I threw up a little... just a bit. But it was enough to make the reg taste bad. I took my reg out of my mouth, put my octopus in my mouth, and swished my reg around and purged it hoping that would clean it out. The instructor saw this of course and came over to make sure I was okay. I signaled back "okay" and he watched me a bit and then we continued on.
When we got back to shore from that dive, he said he realized I wasn't holding my breath, I was just relaxed. He also asked me why I did what I did with my reg and I said, "oh, I just threw up and was cleaning it out."
We calculated our SAC rates on the beach. Mine was really good and he told me that SAC rate was like someone who had been diving for a while. He said that, combined with the calmness in which I handled the vomiting, lead him think I must be a natural for diving
I still keep in touch with my basic instructor (and take classes from him). And he remembers my first open water experience too! Guess I made an impression.