SHG measurements are conducted on thin samples of the antiferromagnet AgCrP2Se6, obtained through a process of exfoliation. The intensity of the response varies with different thicknesses of AgCrP2Se6 flakes, as predicted by numerical models, in contrast with the result obtained from the thick sample approximation, which can be solved analytically. The difference in SHG intensities is attributed to: 1) Fabry-Perot cavity effects (constructive or destructive interference of the electric field inside the sample), 2) surface reconstruction (surface layer is reconfigured, breaking C3 symmetry), 3) edge effects (experimental data shows that there are “hot spots” in the edges of the samples).