Below are the steps that we take to put on a shoulder rest. Notice there is a "big" end and a "small" end. When putting the shoulder rest on the violin, the big end should be under the chin rest.
Put the "big" side on first, then slide the smaller side down the violin to where the wood edge is biggest. This should make a nice tight fit.
First place BIG end under chin rest
Then slide SMALL end onto violin
You should see the shoulder rest make a smile instead of a frown!
Below is the wrong way to put the shoulder rest on the violin.
This shoulder rest has a frowny face (upside down)