I always get a sinking feeling (no pun intended) when I read posts like these! I'm sure I'm not the only one. Even a cheap boat is a huge investment, in money and time, not to mention the way boat ownership ends up dominating your life. Yet time and again, we get newcomers asking questions which should have been asked at the very beginning of a long period of research and education, but they've already bought the boat!
However, in the spirit of helpfulness, to answer your questions:
1)what do I need to do to ensure the boat will pass?
You can't ensure it will pass, and you should have got a valid BSS before buying. Why didn't you get the previous owner to have it tested? Right now, your best bet is to simply get it tested as soon as possible and then attend to anything it fails on.
2)how do I proof the boat is mine?
This is a question you need to put to the person you bought from. If they haven't even provided you with a receipt or any paperwork then not only do you not have any proof it's yours, but you also don't know that it was their boat to sell.
3) is there any canal were i csn keep my boat until i get everything ready?
Once you have your BSS and your licence and insurance, you can legally keep your boat on any canal which is under the control of the Canal and River Trust. (This includes most of canals around London, except the Basingstoke Canal. You will need to comply with the rules for boaters without a home mooring. See here : https://canalrivertrust.org.uk/media/original/633.pdf or you will need to pay for a permanent mooring. Permanent moorings are run by Canal and River Trust and by private businesses. Around London they are in very short supply with people waiting many years to get one. In other parts of the country you can usually get a mooring quite easily by ringing round a few places. Try googling moorings in different areas. Again, you should have researched all this BEFORE you bought a boat.
I appreciate that it's all a bit late for you, but hopefully other potential buyer might read this thread and learn from your mistakes.