Might be a sim issue in which case, who knows...
To rule out human error... What was your SPI? was it a steer point, TGP LOS, a mark point? Any CCRP delivery is going to go to your SPI, so if the bomb is falling somewhere other than expected it's possible your SPI is either A) not what you intend it to be (remedied by checking the bottom left of your HUD, it will say STPT, MARK, TGP, TAD before you drop) or B) You have the correct SPI but it's not as accurate as you need it to be.
If you are dropping on STPT SPI a good technique is to verify you have the right STPT called up, and CHINA HAT AFT LONG to slave your TGP to the STPT. If the TGP is not on your target when you do that, it means your STPT is not where you want it to be.
If your dropping TGP LOS SPI make sure you are lasing when you release so that you are dropping with the most updated coordinate possible. If you want to drop a 54 like a 38 you can immediatley cease lasing after the bomb leaves the jet.
If you are dropping on a markpoint, make sure you were lasing when you took the mark to get the best coords.
Also weapons have required times of fall so make sure you aren't really low when you're trying to drop your PGMS, mid-teens should work.