A friend of mine was in the same situation and mac told him that the only programs that still accept students in the summer are Social Sciences and Humanities.
You can always come back for a fifth year in high school and apply again. That way you have a very good chance at making it to a program of your choice.
Note: If you want to do that option, don't just come back for a fifth year and do nothing, take math and few science courses (like chem & bio),that way, when you go to university next year some info is still fresh in your mind.
Note #2: If you are interested in engineering, make sure you take some computer courses in your fifth year. Try to take programming and some courses like AutoCAD. You will thank yourself later on when you go to university
If you really want to go to university this September, apply to different schools. Check which ones still accept students now and apply.
Good luck