You'll get used to it. I felt my bike was squirrelly at first--my prior bike experience was the bike I had as a kid and the DangerBike that my friend lent to me to get used to riding a bike again.

I think "comfortable" means different things. I got used to the bike's handling quickly, after 20 or 30 miles. I got a lot more comfortable (in both senses) after I got a new saddle. (That helped with the death grip and sore arms.) I can stand for about five pedal strokes before feeling wobbly. I'm still getting comfortable with taking my hands off the bars for more than a few seconds. Grabbing a water bottle while riding is not going to happen. Don't worry too much. Just keep riding.