Yeah, you do a fairly high grade to transfer into the CS+X majors. (Transfer into the engineering CS programs is currently impossible.) However, the highest grade required for transfer is A-, for Math&CS and STAT&CS. A B+ is sufficient for the others. But we realize that grades can still be a source of stress.
I don't like the high grade requirements and neither does anyone else in CS. But we don't have the resources to admit everyone who would do well in the major. So some perfectly reasonable students are not going to get in right now.
If you aren't confident about your grades in CS courses, have a backup plan. Take the beginning courses in at least one other major (e.g. the one you're currently in). Another major plus a CS minor is a solid option. Or you could check out other schools whose CS program you could transfer to.
Don't stress out over whether you will or won't get the A. Stress makes you perform less well. Try to put the grade issue out of your mind, as much as you can, and concentrate on doing your best. I know this is hard to do.
It is not the end of the world if you don't get a CS-related major at UIUC. Many people do well with degrees from other places, degrees in other fields with a CS minor. In fact, many CS faculty members here did something else as their undergraduate major.