To ensure a good connection between the wires and the circuit board, treat the copper pads with flux first, then tin them with a light coating of solder. Apply the solder sparingly so you don't accidentally fill the hole.

Position the wires in the holes, and bend them upwards to make soldering a little easier.

My soldering is quite disgusting, but there is no contact between the wires, that's the main thing! Check yours carefully!