This is easy to fix with some homemade paper shims.

Start with a sheet of paper and punch or cut 10mm holes into it. Then cut out the holes to make shims. FWIW- I've done this often enough that I made a punch from a steel chainring bolt ---- sharpened to the outer edge by holding against a conical grinding burr. Once you've made the shims, soak them in oil (any oil) so they cannot later absorb water and they'll outlast the crank,'

From the description, I suspect that you'll need something a bit thicker, ie. a postcard, cereal box, etc.