I understand the anxiety. When I was applying I felt like there was so much to think of and juggle in my application; it sometimes felt like a part time job getting all my materials ready. I found it really helpful remind myself that although MSW programs are competitive, relative to other programs they admit a lot of students. Many grad. programs admit something like 5-10 students a year, but your chances for U of T are quite high. Even if you don't get in the first year, if you keep improving (e.g. gaining more experience) and have a strong application it's likely you'll eventually get in, even if it's the second or third time. I found it comforting to remind myself of that.
Regarding experience, I do not have a BSW and my transition to social work has been quite recent. I did not have any direct paid experience working in a social work setting prior to applying. The experience I did have was volunteer (with some helping-related part time jobs during my undergrad.). And the volunteer hours I accrued prior to applying the second time only amounted to about 7 hours a week (though it seemed like much more when I was juggling them with work, etc.). So I wouldn't worry, at least for U of T, about having paid work experience in the field. They judge your application holistically, so even if you do feel there's a gap in your experience, this will be weighed against other considerations.
I hope that helps somewhat. I'm not sure about the requirements for other programs, but at least for U of T paid experience is an asset, not a requirement.