Thank you for the reassurance guys. Everytime I'm filling out these forms I get visions of federal agents knocking on the door to interrogate me.I certainly hope I am just over anxious about this.
Respectfully, this is an irrational fear: it's something that simply isn't going to happen.
That may or may not be helpful information. If that's all you need to hear to stop worrying about it, great. But our fears and anxieties don't necessarily respond to reason. If this is a persistent and significant anxiety for you that isn't soothed by facts, you might benefit from speaking to a mental health professional. (I hope it's clear that I'm not saying this in a remotely derogatory way; big fan of therapy over here!)
Not to overgeneralize toooo much, but for the most part, the worst things that might happen from filling out a government form incorrectly but in good faith are (1) you might have to speak to somebody on the phone to correct a mistake, or (2) you might have to pay a little more in taxes than you anticipate (thinking specifically of the ACA income estimator here).
Looking at the cited census laws specifically (with the qualification that I'm a lawyer, but not your lawyer), you are totally fine. 13 U.S.C. 221 (titled "Refusal or neglect to answer questions; false answers") says that you can be fined up to $100 for "refus[ing] or willfully neglect[ing] to fill out census questions. You're filling out the form, not refusing or willfully neglecting to fill it out, so you're good there. It also says that you can be fined up to $500 for "willfully giv[ing] any answer that is false." You're good here too, because you're not lying--at worst, you might make a mistake, which isn't illegal. Both types of offenses--neither of which you are committing--are considered infractions (i.e. not even misdemeanors). Later sentencing laws have provided that infractions can be fined up to $5000, but that's the absolute worst that would happen, and you don't need to worry about it because (1) it doesn't ever ever ever happen, and (2) you're not violating the law anyway.