How to make a box bigger on the inside?

Sounds like a doctor who episode, but its a real question. I bought this box for seeds but it's been a pain in the butt. It's just big enough but if I had like .3 inches more, 1/10 an inch per slot, it would work much better. Is there someone I can take it to to hollow it more on the sides without too much effort, or is there a tool I can use to do it myself... its to hard to get seeds in and out. Danks.

Sounds like a doctor who episode, but its a real question. I bought this box for seeds but it's been a pain in the butt. It's just big enough but if I had like .3 inches more, 1/10 an inch per slot, it would work much better. Is there someone I can take it to to hollow it more on the sides without too much effort, or is there a tool I can use to do it myself... its to hard to get seeds in and out. Danks.