Well, first of all you have to think about your grounds for appeal. You need to show that either the Court did not have all relevant information, AND that if it did have that info, that the decision would have been different, OR that the decision of the judge was "plainly wrong", ie that he or she did not apply the law correctly.
Simply not agreeing with the Judge is not enough to successfully appeal.
If you do think you have strong grounds, then you need to make an application for leave to apply out of time. You can probably find a precedent by googling "appeal out of time, Children Act".
There'll be a fee payable, but if you're on a low income you can file an EX-something (you can down load it from the Court website. It's an application to be exempt from paying the fees.
If you'd like to post a bit more info I can tell you what your chances are, but you have to be absolutely honest about what Cafcass recommended and on what basis. If you are unsure about why judgement went against you, you can either ask the court for a transcript (which costs quite a lot and takes quite a while), or ask your former solicitors for their version, based on their handwritten note. I always send the client the latter whatever the result, as people often don't really take in what the judge is saying, feelings are always running high.