With 40 stitches you should be working 2 k 2 p and seamlessly go around. So that shall be ok. (did you REALLY have 40? Or maybe 41 or 39? If so, you might have gotten offset by that.)
And on the side: Do not work in the round with the stitches on only 2 needles! That is not good for the outcome. You put too much stress on the stitches that are on the ends and end up getting ladders (lose stitches that make a nasty visible line)
if you work with a set of 4 needles, put your stitches on 3 needles. I think people either put 1/3 on each needle or put 50% on one needle and another 25 % and 25 % on the other 2.
I usually work with 4 needles in the stitches and the 5th to work with, but not all sets are sold with 5 needles, at least in the US.
The shape you work in when knitting does not stay in the knit fabric. The tube will just be round, once the needles are out. Do not worry.
Good luck on your project!