when mapping try and find a pattern, map the bottom line first, so no boost just foot on the throttle and hold it at different mapping points,

when you have the first mapping point perfect, look at the next one, it is going to need more fuel obviously so give it some more, then take the engine revs to the next point and adjust fuelling untill its correct

now you can see the jump between them two points, its going to be similar all the way along so add the differece on top of the next point (for a rough estimate), just keep working your way along untill you have all the off boost point nice.

mapping in car is difficult, its much easier on a dyno as you can hold the revs and boost at any point for however long you need, but its not the cheapest way unfortunately !