Just built my first PC and it won't POST, I think I messed up the RAM slots or something

Hey guys, I finally put together my first gaming rig but when I hit the power button, nothing happens. No beeps, no display, just dead. I used a B550 motherboard and 16GB DDR4 RAM, but I read somewhere that you need to put RAM in specific slots for it to POST. I think I might have put the RAM in the wrong slots? Also, I didn't plug in the CPU power connector properly, maybe that's why? Any advice on what to check first? Thanks in advance, really hoping I didn't fry anything.

- buildapc