Move your battery back as far as possible - if needed, CA a velcro strip in back of the servo tray AND to the bottom of the battery pack to hold it in place. You have a "clamp type" motor mount. Loosen the clamps and slide the engine back as far as you can in the motor mount - put the rear edge of the mounting lug on the engine LIGHTLY against the rear hold down bolt before re tightening the motor mount.

If you still need more, use the rear hole in the motor mount to secure the engine through the mounting lug and drill a new front hole through the motor mount (you will be using the mounting lugs on the engine instead of the clamp) and use bolts with NYLON STOP NUTS AND WASHERS. If you have to go this route, MAKE SURE BEFORE YOU DRILL ANY ADDITIONAL HOLES, that the prop has adequate clearance on the front of the plane AND the fuel line/pressure line are not kinked and are accessible for fueling.

A TIP ON THE SUPERSTAR: Do not set the throws on the control surfaces to the book specifications - Set them for MINIMUM throws. This means moving the push rods IN closer at the servo and further OUT on the control horns. As you flying skill improves, you can readjust the control surfaces for more throw.