I have a toadstool (Can check out my gallery). When 1st introduced in the tank, it will bend to one side a bit typically and begin a molt process (Might notice some red/deep red at the base to mid section). 2 to 4 days later he should be upright and you should see some 'snot' looking material coming off of him. This is normal and happens every so often. You can expect he will cycle through this as he adapts to the new environment. 260w (About 4.5w/g) should do in a 55, though you don't mention your lighting specs (2 x actinic 03
's? 2 x Actinic white? etc) so hard to say if you have the right kind of lighting. No tag line, so I can't tell if this is your 1st coral or what. However, before you run out and start treating the tank for untested problems, you should check your parms. As for too much light, I run 440w over my 75G (Again, see gallery) and as you can see, he's all about some actinic 440w light, so your not in jeporday of 'over' lighting. How big is this guy? Was it mounted to start with? One of thie biggest probs with leather corals is that they will expand and contract (ne1 ever try to glue finger leather..pfe, pain in arse) and can negate glueing efforts. Rubber bands will sometimes only cause them to start to divide once they expand again. I have not personally tried this but you can try nylons (Or similar). Cut some nylons so the base rock and the coral will fit, but tight enough to keep him from getting too far off the rock, if at all. You can then rubber band the nylon around the two and he should be able to still get light. I have seen this suggested elsewhere, but I have never tried it. Although, if you have been messing with this guy a good bit recently, best to just let him sit a week or so. Once he starts perking up, you can have another go at him!
Best of luck!