If you cut a 3" X 3" Square, then you can use Stampin' Up!'s 1 3/8" Square Punch to make a PERFECT FRAME. Just insert the punch in ALL THE WAY, and CENTER it visually in the punch; like this...
Use the frame to make a shaker card like this one; created a LONG time ago...
Or this card I made for a Sell-a-bration swap... That's a 1 1/4" Square that's fitting perfectly inside that easy-peasy frame!
And remember this project from way back when? While those are 1 3/8" CIRCLES not squares... it works just the same! Try this trick on your 3" X 3" note cards!
Hope this helps you create some quick and easy layouts!
