Does your crank bolt look like this?

One key with pin spanner holes.
You do not need to remove the ring to tighten the crank bolt. It sounds like there was inadequate torque used for assembly. After checking for damage to the tapers as recommended in the previous posts, you'll want to grease your crank bolt threads and reassemble. Shimano one key release torque values with 8mm Allen bolts are up to 400 in/lbs, or as tight as axle nuts are supposed to be. You will need to get the crank bolt as tight as you can. You're unlikely to snap the bolt with an L shaped wrench alone.