Stupid question time, do you buy back carbs by exercising? E.g. If I'm working to 50g of carbs, I have weetabix at 26g leaving 24g for the rest of the day, if I workout will I be allowed more carbs?
Don't look at it this way, using words like "allowed" and "buy back" - don't see boundaries and limits. Set a reasonable daily carb total that is something you can easily meet (when you've stripped out the basic high-carb stuff like bread, cereal, potatoes, rice, pasta) and then aim to get close to it. If you're 10g over or 20g under it doesn't matter at first - you're giving yourself a guideline and changing your lifestyle to improve your health and control your illness.
Over time, as you get the hang of things and discover new foods to eat (and, without carbs, your appetite will also lessen), you'll find yourself eating fewer and fewer carbs and your daily total will only need a slight conscious nudge to reduce. Eventually you'll hit a point where you're comfortable with what you're eating and able to control your BG at the same time. But it's a journey, not a single switch and you shouldn't feel in opposition either with your body or with your food.
Take it gently, over time and keep a food diary which will help you understand your eating trends and how they impact your BG.
Good luck!