mixing paint

I painted a room with a blue latex, semi gloss. The blue came out a little too dark and a little too shiney. I have a 1/2 gallon of flat white, same brand. If I mix it with the 1/2 gallon of blue semi gloss that I have left will it work OK? Can I just paint over the semi gloss on the wall, or will the mix not stick well?


Thanks for comments!