Two possibilities. Neither of them are that your frame is actually BB30.
1 - your shell width is wider than spec. PF30 cranks tolerate this, GXP not so much.
2 - the cups didn't go in perfectly straight, so everything is a bit tight.
Easiest way to tell for 1 is to eyeball the gap if any between the spider and the drive side cup. No gap at all? Probably a bit squished.
For 2, if there is a gap between the spider and the cup, but everything is still a bit tight, then it's possible the cups aren't in right. How did you fit them? You need to do both at the same time with a quality press for it to work.