The next step is to install the stem and backbone.   Fit these parts in the slots that have been pre-cut to receive them.   The stem will need temporary support until the battens are installed.   Take check measurements to make sure the stem is in the correct position, relative to the sheer line and the centre line of the hull.   At this stage, the biggest mistake you can make is to have the stem off the centre line of the hull.   Check everything against the centre string line and use plumb-bobs, a large square and tape or ruler to make absolutely sure everything is correctly located.