Did you prime it? Are you sure you used the right roller? I prefer a satin finish on ceilings for just a tad less reflectivity. I'm sure some paint pros will chime in here.

Did you roll with the sun? That can make a difference. If the sun comes in the window and hits the roller lap marks perpendicularly they will show.

Roller technique would be critical in this instance. You would need to be sure to feather the edges while still wet. Doing only one section at a time taking care to finish each section while the paint was still wet. In dry conditions I have been known to thin out the paint a bit in order to keep it wet long enough to feather.

Do you perhaps need another coat of paint or have you already done two?

Like decoenthusiaste says, semi-gloss leaves very little room for error.

Thank you! I used the semi gloss because I wanted the ceiling to look like wood, like wainscoting. What do you think if I painted the squares eggshell and left the wood semi. Too much going on? Thanks for your input.

It's worth a try. Eggshell being the lowest level of gloss? I would go the lowest level of gloss for the paint line.

It's hard to tell from your pictures so this might not really apply...but in the first picture it looks like the finish is uneven. This happens when you use a higher gloss on a porous surface like sheetrock. So with a coat of eggshell on top of what you have already done you might get away with one coat but don't be surprised if it takes more than one. Because it is on sheetrock it will never look "perfect" but it can look pretty good.

Also the paint should stay wet longer because it is lying on top of a semi gloss finish and not soaking in as much.

Work one section at a time and be quick about it and I bet you get a big improvement!

Good luck!

Have you considered a light sanding with a fine grit between coats of paint.? It is a beautiful ceiling and room.