While you are aiming for a slightly gooey centre, it being too runny is not want you want.
This is a common problem caused by insufficient draining and drying of the curds before moving the cheese to the ageing stage.
Drying is a very important step because too much moisture will accelerate the protein breakdown throughout the whole cheese. The protein breakdown happens naturally and begins near the rind where the white mould is growing. Your cheese might look dry on the outside before you start ageing but make sure you follow the instructions to ensure it is the correct moisture throughout the cheese. If the inside is too moist it will result in a runny overripe cheese.
Make sure the draining area stays in the 21-23°C (70-73°F) range and that your drying time is sufficient to get rid of any residual moisture.