First full bike build – crank arms not symmetrical, what did I mess up?

Hi everyone!

I’ve recently started building a bike from scratch using parts I had on hand — with all the trial and error that comes from being a beginner in bike mechanics like me.

I’m using an FSA Gossamer Pro AGX+ 46/30 crankset with the following specs:

• 24mm hollow spindle
• FSA Direct Mount
• 46/30T chainrings
• 47mm chainline
• 154mm Q-factor

The bottom bracket is a Shimano Hollowtech II MT501B 68/73mm, also for a 24mm spindle.
The frame is steel (Fluide Cypress Expert), and the bottom bracket shell measures 68mm.

On paper, everything seems compatible. The crankset fits and installation went smoothly — but I’m facing an issue: there’s a noticeable asymmetry between the left and right crank arms relative to the frame.

I removed the 2.5mm spacer on the drive side and installed a 1.5mm spacer on the non-drive side. Right now, I have roughly:

• ~5mm clearance between the left crank arm and the frame
• ~10mm clearance on the right crank arm side, so about a 5mm offset.

Also worth mentioning: there’s a wave washer on the drive side of the spindle.

My questions:

• Are the bottom bracket spacers mandatory in this setup?
• Could the wave washer be responsible for this offset?
• Could it be normal to have such a difference ?

I’m a bit stuck and out of ideas, so I’m turning to you knowledgeable folks — any advice or insight would be deeply appreciated!

Thanks a lot in advance 💜
Paul