i would agree with everyone else i, afraid, but if you feel you should get more, write to them and ask them for more, say you feel £100 is not enough.
however if you think you are on for the big bucks here, then think again... i woudl not go higher than £150... £200 at a push... but i think you will be lucky.
you must also photograph the area... if there is a jagged piece of metal sticking out then you will need evidence of it... but if really you had your hand in a place where you really shouldnt have, then you are going to struggle to prove negligence...
were you climbing the shelf, reaching up and clinging onto the underside or something?
if so then you really shouldnt have...
as someone said, if they warn you to get help and you didnt then, you had fair warning and chose to proceed...your fault...