Mulch mixed in soil
I'm a novice gardener who's trying out square foot gardening for the first time in a raised bed ( 4'x4'x13"deep). I'm afraid I messed up when adding/mixing my soil... I mixed in 2 cubic feet of pine bark mulch into the soil thinking that would help air out the the soil and improve root growth. Later I read in a thread that was bad because it will rob all the nitrogen from my plants as they decompose. How bad did I mess up if at all? I'm basically using " Mel's mix" and just added the 2 cubic ft of mulch along with it...
A very simple combination for most garden beds is 50 % screened top soil and 50% compost.
Both of these materials are readily available, inexpensive and easily transported to your garden.
The Mel's Mix you mention is essentially a potting soil, suitable for potting container plants.
Don't worry, the beauty of raised bed gardening is that it is quite easy to fix! Well, I can say that because I'm not the one that will have to shovel out the pine chips!
Here are some articles to help you get started.