Robertson screws
The "Square" drive screws you have are called Robertson screws up here in Canada.
I am amazed that a kit manufacturer would be so blind as to include a fastener that can only be utilized in a very small part of the world.
All of our kits use common Philips screws.
The good news is that a Torx bit will fit in the the head of the screw and allow you to use it. I discoverd this at a fly in in California when I found I forgot the correct size Robertson screwdriver back home.
Check your tool box for some small Torx bits.
You can also use a small slot screwdriver that fits between the corners of the square.
I hope this keeps you building.
Peter