You haven't ruined it - it probably will knock you out of ketosis, depending on your body, everyone is different. The good news is that if you do get out of ketosis it will only be by a little, so don't go eating more carbs otherwise it really will be a problem. Get right back to it and you'll be back in keto again within 24 hours most likely (vs at least 5 days starting from scratch). You can speed up eliminating any carbs from your system by doing some (vigorous!) workout/activities to burn off any glycogen your body has laid down, it doesn't need to be lengthy exercise but it does need to be something that really makes you work your muscles - otherwise, just don't worry, draw a line under it and move on.