If you did a fresh IVF transfer, you're probably extra bloated from your swollen ovaries. Plus, if you're on supplemental meds (estrogen and progesterone), those can cause extra fluid retention.
If you did a single embryo transfer, I believe the likelihood of it splitting into identical twins is somewhere in the range of <1% to 3%, depending on factors like age, the procedures you had done (I think assisted hatching can increase the identical twin rate), or what study you read. So pretty low.
Either way, good luck with the ultrasound on Friday!