I looked up G & B potting soil. Do you have your bag the soil came in? What I could come up with is that they might have added water holding 'gels' or 'sponges' in the soil. The other thing I found is that it had kelp worm castings and compost added. This needs to be added to your citrus fertilizer amounts or you could easily go over the chemical (nutrient/fertilizer) limits for your plant and kill it.
What I am seeing doesn't match too little fertilizer or too much fertilizer. Not a happy plant.
Could be too wet like you are thinking. If you have only watered it once and it seems saturated and heavy still...you are probably right. Did you put just soil in that pot or did you put gravel and rock at the bottom of the soil above the drainage hole? If so, I'd dump the soil out right now and repot with different potting soil; no water holding gimmicks like the sponges or gels. No fertilizer and the organic additives should have been sterilized with the rest of the soil. You will have to add fertilizer balanced fertilizer but for now let's deal with the saturated soil.
Tell me how you planted your plant, did you add just soil to that pot or did you add gravel at the bottom of the soil? Tell me the formulation of the citrus fertilizer you used. If you can find that bag, tell me the NPK proportions that should be on the bag. Otherwise describe in more detail the components of the soil. Looks like it should be a great soil but I am against those water holding gimmicks.
Please give more information. Leaf curl is normal in an effort to protect the leaf from too much evaporation and heat.
Where did you find this plant before you purchased it? Was it in doors or out doors? I am assuming it is out doors now. If it wasn't acclimated to the out of doors that might be why it is trying to protect itself from too much light, heat.