Hi Tracey,
Welcome to the forum!
Yes, scheduling is a difficult part of the business, especially at first. There are a few things you can do to become more efficient.
1) Sign up with more companies. This will get you more opportunities. Yes, you will have to check more job boards. But you can get more efficient at this with some tips.
2) Learn when to check the job boards. Some companies offer shops at predictable times of the month. Figure this out and create a job-board calender for yourself then be sure to check the companies on those days. If you can't figure it out, ask the scheduler. Tell them you want to do more of their shops, but need to know when to check.
3) Check the job boards that are most relevant to you first. Those are the ones that have shops in your area that you want to do. For a tip, see #4.
4) Use the 'open all in tabs' feature in Firefox, combined with bookmark folders. For me, I create bookmark folders based on my preferences for companies. For example, the folder in my bookmark toolbar called 'MS-1' has all my best companies. These are companies that have lots of shops in my area that I like to do. "MS-2" has some more companies that are not quite as preferred. "MS-3" has the next tier and so on. When I want to check job boards, I go the the 'MS-1' folder and click 'open all in tabs.' Firefox opens all the bookmarks and I can go to each quickly after they load. Saving passwords in the browser speeds things along. When I am done with this group, I can stop or go to 'MS-2' and do the same.
Good luck and have fun!
Happily shopping Rhode Island and nearby Massachusetts and Connecticut