As with pretty much any model construction, the accuracy or straightness of the finished product is only as good as the board or bench upon which it's built. That said, "do yourself a favour" and ensure your building board or surface is flat and straight. The dividends paid in a better flying model are worth the expenditure on a nice flat surface.
For this build, I will use some medium density fibreboard or abreviated as "MDF" sheeting to construct each surface on and also for compressing the balsa sheeting onto the finished framework structure. The MDF will be cut into sections a little bigger than the plan form of the wing and stab jigs. See photo below.