if this is the heatbed you've got, then you've actually got a decent sized PCB heater on an aluminium plate under the glass. In that case, most of the heat loss is more likely due to the geometry (edges and corners area always easy to cool, hard to heat). The gold coloured tape in the middle just holds the thermistor in place. https://www.creality3dofficial.com/p...-hot-bed-board

Most printbeds have a temperature variation. You could try bumping the temp to compensate for edges to see if it sticks better. If it still doesn't, then heat up the bed and check it's still actually flat.