If a business asks you to work more than 10 hours a week, then you can politely decline. According to the Labour Contract signed by both parties, the apprentice is only required to work for 10 hours a week. Anything more than that is up to you.
During the onboarding process, you and your mentor should have already decided upon a set working schedule. If you are suddenly being asked to do more work than you can do, then talk to your mentor about it and tell him/her nicely that you are not obligated to do any work outside of what is stipulated in your contract.
On the other side of that coin, doing more work might mean more learning opportunities for you. The final decision is really your call, but make sure that both parties are either adhering to the signed Labour Contract or in mutual agreement to make small changes to it.