You can extend your status as a Visitor in Canada without leaving if you want to make 100% sure you will be allowed to stay..Fill out IMM 1249..http://www.cic.gc.ca/english/information/applications/visitor.asp
You still have time to apply..it says 30 days before your status expires but they will not penalize you for sending it closer to your status expiry date just make sure its before 13th August..
You will automatically have implied status until a decision is made (it will give you about 80 days)
If you really want to get on your flight you can come back in 2 weeks time the length of time required is 48 hours, When I extended my stay I put that my Husband is supporting me...I added;
- Photocopy of 3 most recent payslips
- A copy of his letter of employment
- A photocopy of his option C Printout..
If you wish to support yourself you need $10,000 + for 6 months..a letter from your girlfriend showing she is willing to support you would be a good idea..
Hope this helps you..