Which version of LR are you using?
What is your OS?
Just to make sure: You're exporting to jpg and you did check the box next to field for the size?
Try setting the file size to a maximum of 2500K and see what happens.
2015 2.1 version of Lightroom CC
I'm using an iMac, El Capitan OS 10.11.1
I'm exporting to jpg and yes, I did check the box next to the field for the size. It still comes out larger for some reason.
I'll try a lower setting ... I'm sure that'll do the trick. I just wondered why setting it to 3000 K didn't work.
Ah ... it has something to do with setting the long edge too high ... but I want the quality to be good enough for perusal. Hm. Maybe that doesn't matter? (Sorry, I'm pretty darn clueless. Sigh.)
Setting the long edge (if it is big enough) and specifying the file size must be less than 3MB are opposites. You can't really achieve both.
Trying to increase the quality, while also specifying a maximum file size of 3MB, are also opposites. You can't really achieve both.
When you do get an exported photo with file size that is less than 3MB, just look at it with your own eyes and see if the quality is "good enough" or not.
Honestly, these days, I don't really know why anyone would specify a maximum file size of 3MB, you can move much bigger files around without causing any problems, and relatively quickly. Ten years ago, this statement was not true.
Thanks for the explanation, dj_page!
AS I said, I really know nothing about this sort of thing. It's time I learn, I'm sure, but my brain is in a muddle! (Typical of me, really.)