You can definitely fundraise beyond your original campaign goal!
All funds raised during the duration of a successful campaign will belong to you.
If your project exceeds its original goal, you may want to consider how you will communicate with your existing supporters in terms of what it means for the project. Will there be more shots, new songs, better artwork?
It's always a good practice to take the time to explain your intentions and plans for any extra funds.
There are no hidden or additional costs associated with overfunding, beyond normal payment processing fees.