heater bed oversized too much?

[Bruce19]

, I ordered and received 310 x 310 120v 750 watt heater with 4 holes for my 3d printer. I also installed a SSR to power it. my bed is exactly 300mm x 300mm so the heater pad sticks out 5mm on all 4 sides. It clears the Z towers with plenty of clearance. My question is 1) is it safe to run like this? 2)will it have an adverse effect on heating the bed uniformly? and 3) can I trim the 5 mm off?