Uh, yeah, so what?
If they have the evidence to prove you committed a crime, then they have the evidence to prove you committed a crime. It kind of makes sense that they'd, y'know, prosecute you for that crime.
They can't just arbitrarily increase your sentence based on the suspicion of another crime. There are statutory limits for the crimes they can prove, augmented by sentencing guidelines. The court cannot exceed the statutory limits, and deviations from the sentencing guidelines require a justification to be articulated. "I think you also did W" is not a valid justification.
You're always at risk of a harsh sentence for whatever crimes can be proven. If you're not prepared to take that risk, you should probably avoid committing the crimes in the first place, no?