A check with set-squares (you can sub a box of cornflakes in extremis) reveals how I omitted to check if the dimensions at the upper end matched those at the lower.
This is not to be overlooked, as if the gap here is too small it won't accommodate a fourth panel that completes the box. Yes, you can trim the panel to suit, but getting it right at this stage will leave you basking in a warm glow.
Do this while the adhesive is still pliable, and you will find it will give a little without needing to be smoothed over again with the crafting (viz. kitchen) knife.
Top tip: don't apply too much adhesive at the joint along the floor of the box as the chances are you'll stick it to the floor. Do it in the lounge and you're walking around it in perpetuity, though it does make for the perfect conversation-starter at parties.
