Modifiers Adding Even When Manually Updating Spell

I use quite a few cantrips and other spells that do not add my spellcasting modifier to the damage, but when I use the spells in game they keep adding my modifier. I go into the spells manually when I use them to change them, making sure the save DC is correct, or the ranged attack roll, and I always make sure the damage is correct, but even when I manually update the spell it continues to add the modifier on a hit. I then have to manually go into the enemy and give them back the HP. This is especially annoying when the extra damage kills the enemy after a long-fought battle. It takes away from the epic fight and makes it feel like a cheat.