Use a warm knife and press downward on the sides. You'll be surprised how spreadable the curds are with enough pressure. Once you have a feel for the sides, you can judge how much pressure you can put on the top and bottom. That said, it looks like you may have your curds a little drier than called for. I did that the first time or two. If you can't get the exterior completely closed it will be OK, just different. You may find the finished result a bit drier than a true Stilton, but still tasty.
Start another in a few weeks leaving the curds with a bit more whey (stir less). That will help ensure you have a constant supply of blue cheese, whether Stilton or not.