Bath waste not water tight after replacing.

[idrinktea]

I am having a problems with a relatively straight forward job, the nut that connects to the screw for the plughole broke/vanished and the bath started leaking. I replaced the whole waste/overflow with a new one of the same type, however, when I'm trying to get it aligned with the bath hole, and get it screwed in, the plastic and rubber seal seem to be bending down a bit on one side, leaving a small gap. I am having trouble getting rid of the gap and get this water tight, I also have some silicone handy as well. (bad diagrams below)

Can someone please advice how to resolve this?

 

[terryplumb]

Pictures of the actual waste connected under the bath would be helpful.

 

[idrinktea]

Pictures of the actual waste connected under the bath would be helpful.

I will do, sadly at work just now.