I decided to through the Firebolt cantrip into the "Attacks and Spellcasting" box on the character sheet. I understand I use my Char modifier, but do I also apply a proficiency bonus as well to the Atk bonus? Thanks in advance.
For cantrips and other spells, both the spell save DC and spell attack modifier include proficiency bonus.
If you check the sorcerer's Spellcasting rules, it tells you how to calculate your spell save DC and your spell attack modifier.
Spell save DC = 8 + your proficiency bonus + your Charisma modifier
Spell attack modifier = your proficiency bonus + your Charisma modifier
Your character's proficiency bonus is included in both formulas.
Cantrips are spells. When you make an attack roll as part of a sorcerer spell, then it's a spell attack, so you roll a d20 and add your Spell attack modifier, comparing the total versus their AC. However, the proficiency bonus is not usually included in damage rolls.
Similarly, if a sorcerer spell requires the target to make a saving throw, then the target would roll their saving throw (d20 + some modifiers) against your spell save DC.