Raised bed soil question

First year doing a raised bed and I used 1/3 peat, 1/3 black cow, 1/3 top soil. I’ve noticed that the top layer of my bed forms a crust after it dries out and I was wondering if this is normal or not?

I layered all of my ingredients straight into the bed and mixed with a shovel and a rake. I measured the peat while it was dry then soaked everything down at the end for a long time. My soil level looks good so I think I measured it all correctly.

I’ve got lettuce in the bed right now and it’s slowly taking off, just wondering about the crusty layer and if it’s common. I’ve not mulched the bed either. Thank you all for any help!