Might be worth checking tr1 for straightness by looking down the length as a slight bow may account for the slight discrepancy. Seeing your pics jogged my memory that a couple of pieces of mine seemed to be a little out even tho everything was cut pretty much bang on and this was down to some of my steel being slightly bowed
Is it the same situation on both sides?
Those tacks are a touch too big so will have twisted things a bit but im sure you will sort it
just a tiny tack on opposite corners is enough at this stage, its supprising how strong it becomes once triangulated even with tiny tacks
