Reasonably flat will work fine. You can trim the comb with a serrated knife to keep it in line. If it is warm enough you can gently bend the comb straighter, if it is not too crooked. The biggest thing is to make sure that the comb is put in with the top in the same position as originally since the cells are angled slightly upwards. The smaller worker comb should be in the center of the nest with the larger drone comb to the outside. The bees will connect everything together in no time.