The whole point of the resources is to help you improve: financially and sustainably.
There is a strong, well-evidenced link between behaving more like a B Corp and improved financial results. (See: What data and evidence is there for a "better", more purpose-driven way of doing business?) Waiting until you feel you have more financial room to do good is to overlook the potential the BIA and other B Corp resources have to help you reach your financial targets. The BIA is like an organisational excellence framework; regardless of whether you want to certify or not.
It is with good reason that an ever-increasing number of private equity and venture capital investors are using B Corp resources to improve the performance and lower the risks of their investments. (See: Who is investing in B Corps?)
A better question is to ask what the risk of staying where you are is?
Not trying to change risks you being exposed and lacking stakeholder relevance - from how willing your employees are to show up and excel to how well respected your brand is in the marketplace.
It is true that to certify you will need to have achieved a certain degree of sustainable excellence; which you may or may not have at this point in time. But the BIA is designed to help you get there, not simply prevent you from joining if you aren't there yet.
But the B Corp model isn't, of course, promising perfection or a bulletproof business. Yes, the data shows it is a good thing to do; that it is a better choice than business as usual. But every business still has the potential to make bad choices.