Bath help

Bath needs a good bead of silicon between the top edge and the wall. If it's wobbling, then check the feet are adjusted properly and screwed to the floor. I usually screw a piece of timber across and under the feet first

 

If the feet are adjusted and screwed to the floor and the bath edges have been bedded onto wall with plenty of silicon and it's still moving, have you used any 'L' shaped brackets that may have come with the bath

Not sure what you mean when you say there's nothing for the screws to screw into ?

Usually some timber baton set into bath during manufactur for securing brackets

I'm diy so only fitted 2 or 3 baths but I always baton the wall as well and the bath sits on these timbers, again with L brackets and plenty of sili - it won't move

 

As Dave said, are there any L brackets? I always trial fit a bath first and make sure walls drilled and plugged and feet adjusted before I silicon it in. You can usually move the brackets to a solid part of the wall. Sometimes you need a bit of ingenuity.