Is a fancy handmade card overkill for a coworker I barely talk to?

Finish it. I made a super detailed card for a coworker I only knew thru hallway chat, and years later she told me it went into the baby book. Handmade stuff for a new baby reads as thoughtful, not over the top, because everyone knows you spent your own evening on it. Nobody on the receiving end says 'this is too much,' they say 'you made this?' The simple stamped card would be the riskier move at this point anyway, since it'd feel like you lost nerve halfway through your own idea.

For the curling problem, the fix is heavier paper and one edge of glue. Cut the little outfits from 80lb or higher cardstock if you're not allready, and give each piece a quick press under a book overnight before assembling. Then attach them with glue only along the top edge, right where the clothespin would sit, and let the bottoms hang free. A thin bead of liquid glue with a fine tip, not a glue stick, holds better and stays hidden. Even better, make tiny clothespins. Cut little rectangles of kraft or white cardstock, snip a notch with scissors, and glue each one over the line and the top of the garment. It covers your glue spot and sells the whole illusion. You can also buy mini wooden pegs at craft stores, they're like a quarter inch and they're adorable. If you want the clothes to look hung rather than glued, run the string across the card front and glue the string down at both ends first, then lay each garment against it and pin it. The garment hangs off the string instead of sitting flat, wich kills the curl entirely. Micro foam dots behind the middle of each piece also work if you want a little dimension.

One thing I'd add, keep what you write inside pretty low key. The card can be elaborate but if the message is short and friendly it won't feel like too much coming from a desk buddy. Something like 'so happy for you guys' is plenty. Also take a photo before you hand it over. I skipped that on a card I spent forever on and I still regret it, all I've got is a fuzzy memory of the thing. And are you putting the name on the front or inside? Front reads bolder, might depend on wheather she's announced it to everyone yet.

Agreeing with the point about keeping the inside message short, that's exactly what saved me on a shower card I made for my neighbor. I went big on the outside with a pop-up stroller and then wrote maybe six words inside, and she never made it weird, she just kept showing people the outside. One thing on the clothesline though, I used baker's twine on mine and the slight fuzz on it actually grips the glue way better than smooth string does. My little onesies stayed flat for once. Also second whoever said finish it, you're two evenings in, quitting now would haunt you.

Hand deliver that one, don't mail it. I put a card with 3D elements through the post once and it arrived looking like it lost a fight with a sorting machine. I prolly send out 40 or so handmade cards a year and anything with pieces sticking past the front face now goes in a padded envelope or gets handed over in person. Yours is going straight to her desk anyway, so you're fine, just don't get tempted to slip it in the internal mail where it'll get stacked under binders. One more thought since you've got the dies out already, cut a spare set of the outfits in white and keep them with your supplies. When her next kid or a shower invite comes around, you'll thank yourself.