Great job on the shaping Shimmix!

You can mark out your pup positions and the mask off around them with tape.
Put a drill hole near one of the corners and use a coping saw to rough out the basic shape, staying well inside your guidelines.
Once you’ve got the bulk of it out you can use your dremel to get closer to the final shape and hand files and small sanding blocks to square every thing up to the final size. It’s either that or get an Ozito trim router or Ryobi 400w from the big green shed. I think th y are about $90.00 at the moment. (I’m assuming you are in Australia here).

The bevel will be tricky without a router, but from memory you can get 45 degree bits for the dremel and a small “router ish” attachment to hold the unit straight up and down. You’d want to set up a very stable work platform and a spacer around your scratch plate to keep the dremel level.