Hi I think the advice you have been given so far is good and you really do need to apply yourself and try to improve those grades, but apart from that, may I suggest that you speak to your dad and apologise for your behaviour so far. This shows that you care what he thinks of you.
Then, try to explain that from a psychological point of view, placing this amount of pressure on you is counter-productive- if you become that terrified of failing because there is so much at stake you won't be able to concentrate properly- you'll be too worked up and it won't help.
Why not make up a rota that shows your 'extra study' time and your 'puppy care' time, then put it somewhere prominent and stick to it! This shows you take all your responsibilities seriously. And do get some help from teachers at school, they really can make a difference (they stopped me failing a science A level I really needed!).
I hope some of this helps- good luck :)