It looks like you pretty much have everything. Remove the trigger assembly and put the rifle back into the stock. Reinstall the trigger assembly. You are probably missing the little spring that goes into the stock, under the rear of the trigger assembly. This will probably allow the receiver to move a little in the stock. You can get replacement springs for under a dollar. You will also need a duckbill magazine like the Tapco as you don't appear to have the fixed 10 round mag. This is a bit harder to find as they are pretty much sold out everywhere now.