Nope, save-scumming is totally fine and won't change anything. What you're seeing is a difficulty fight, some fights can still be lost if you roll low enough. For now the system merely rolls a 1-20, and you have to beat the difficulty rating (10, in this case)
In a future update things like your Health and Armor will play a factor by increasing your roll number. Just keep trying the fight and eventually you will complete it.