Drywall – Toggle bolt stuck in the ceiling with mounting plate

Are you comfortable with cutting the bolt to a length between 2" and 3"? That would be simplest.

Another possibility would be to use another piece of wood between your shelf and the wall to create more thickness for the 3" bolts.

If the concrete is actually concrete block, you can drill into that quite easily with a masonry bit from your local hardware store. If it is an actual poured concrete wall, best not to bother.

ADDED:

To shorten the bolts:

A) Take the bolt to a hardware store, tell someone you want the same bolt but in a 2.5" length - this is likely the easiest thing.

B) Cut the bolts:

1. Thread a nut onto the bolt and spin it back towards the head.
2. Use a hacksaw to cut the bolt (if you clamp it, clamp on the nut and head - not the threads) - OR - use a Dremel with a cut-off wheel - OR - use boltcutters!
3. Unscrew the nut from the bolt; this will clean up the damaged threads where you cut it.

The bigger question is how many vertical supports and how long are they? 1/4" lags 2” into the 2x4 has 510lb pull out strength (255lb/inch) put 2 or 3 in each piece of strut and each one can handle hundreds of pounds. 5/16” lags 266lb/inch; 3/8"lags 305lbs/inch. You don’t need a very big lag bolt when using multiples. My examples have a small safety factor added in and these won’t degrade the strength of the 2x4. I usually drill pilot holes, But not all brands of screws need pilot holes. The depth into the wood is the threaded part that provides the pull out strength over ½" sheetrock I would make sure to have at least ¾" -1” smooth shank that provides the sheer strength as the weak point is the start of the threads.