The "golden rule" is that exposure controls the shadows and development controls the highlights.
If you try to lift shadow densities through development, you will adversely affect the highlights along the way, as the densities on the straight part of the curve (mid-tones, highlights) react more readily to extended development than the tones in the toe of the curve (deep shadows). It will push the higher densities on the straight part into the shoulder of the density curve and you will loose detail there. This is especially true with a developer like Rodinal that has an inherent tendency to build up contrast quickly. By the time you have compensated a two stop lack of light in the shadows through development (if that is possible at all) you will have blown the highlights beyond recovery (unless the tonal range of the scene was very, very limited)
The other "golden rule" is that when tweaking a process you never implement two or more changes at a time. Next time change exposure as suggested by many here and change nothing else. Review the results. THEN, and only then, if you find that shadow detail is good, but overall contrast and tonal separation still lacking, you can extend development time in the next step.