Cut central divider from 1 of the boards using a shorter straightedge. It’s 20mm higher than you may expect to allow for tenons of housing joint.
Corners of table are mitred. To make successful corner mitre joints, cuts must be made at exactly 45° and square across board. For first cut, clamp a straightedge about 110mm from 1 end of board and check with a square.
Lean saw over at 45° and set depth so you can cut all the way through timber. Ideally, make a practice cut first because occasionally 45° marking on saw may be slightly out, and even 1 degree will be noticeable in final result. Make sure saw stays hard against straightedge while cutting.
Check angle is 45° along length using a combination square. Adjust if necessary.
Mark out length of a side (360mm from long point to long point) on laminated pine sheet. With saw unplugged and still set at 45°, measure distance between far side of saw base plate and face of blade (here, 105mm). Measure this distance back from 360mm mark.
Clamp a straightedge to mark you just made, then make cut, making sure board is supported and clamped so it can’t move. Turn offcut over so mitre can be used for top, saving a mitre cut. Cut top, bottom and remaining side in same way.