Awesome. I don't know much about the industry, but do have a background in SaaS inbound strategies and have a few thoughts:
-Around 70 people every month search for "Flat rate pay calculator." People are looking for a solution, but some don't realize that software is the answer. To get in front of these people, consider building out landing pages using keywords like "flat rate pay calculator" and throwing up a copy of your old Excel spreadsheet as a template for them to download. At the bottom of the template you could write something like, "Want to manage all of this without dealing with the hassle of spreadsheets? Click here to check out a free demo of Flat Rate Tracker." Alternatively, you could start an email list by offering the template and nurturing the list. Just depends on your audience.
-Consider creating a company page on Capterra under categories like "auto repair software" and ask your current users to leave a review. If you have a pre-recorded demo video you could throw up on the page, even better.
-Nice, clean homepage. Love that it's not cluttered. Consider diving further into the pain points. For example, your FAQ page is great, especially what you wrote under the FAQ's "Why use Flat Rate Tracker" -- It reminds your audience of the core of their problem, which I assume is getting paid correctly. The big takeaway is that mistakes in their flat hours is costing them money, which is why they need your software. Why not make it a tagline on the homepage? Something like "Mistakes in flat rate hours leads to manual error and lost money. Track your hours quickly and easily and avoid costly mistakes with Flat Rate Tracker."
-If you have a picture to go with your customer testimonial, it might add more trust to the testimonial and humanize the page.
-Again, I don't know much about the industry, but it might be worthwhile to experiment with a "Book a free demo" button. Some industries prefer talking to a real person before trying it out, while others like to dive right in. Including a demo button will help you reach those who prefer calls.
Just a few off the top of my head. Hope this helps.