You can be a little off centre without too much problem, but if you go too far the bow will try to twist in your hand (Torque).
One trick is to angle the grip slightly so the top of the grip is more right than the bottom of the grip. This can get you nearer centre shot while leaving your arm out of the way. The thing to consider is where your hand presses on the bow, that wants to be in line with the tips and the string line is ideal also in line with the tips, everything else can go where it likes within reason.
I like to dangle a bow from it's nocking point on the string and look at how it lines up... using a plumb bob to check the vertical.
A picture is worth a thousand words, so have a look at this post on my blog showing string alignment on a bow with some limb twist.
http://bowyersdiary.blogspot.co.uk/2012/10/maple-finished-hazel-bark-on-bow.htmlYou can see I have it slightly off centre for a right handed archer, but it's still well within the grip.
Del