The only way to be on top of your budget is to keep checking it, and to be extremely honest about costs.
You will need to treat planning your wedding like a job, if you go over budget there will be consequences. Fill in your budget planner weekly, noting down when deposits have been paid and when final amounts are due. If you update it regularly and always have it to hand when you visit suppliers then you should be fine.
Do not buy anything that is not budgeted for on the list, and always check if VAT is included.