First of all, you don't have multiple H1Bs. You have a approval for "change of employer". Multiple H1Bs means you can work for more than one employer at one time for the specified hours per week for each employer. You cannot work for both of these A and B at the same time but can work for either A or B. "change of employer" takes effect if you work at B, then you cannot work for A without another transfer from B to A.

If it were the case that a person couldn't work for company A as soon as "change of employer" to company B is approved then all of H1B will have to switch job without giving notice to company A. Which is not the case. When I did, I joined B after 1 month of approval. I applied for GC and got that too. If it can be done after 1 month, it can be done after 3 months.

Remember, you ddin't sign any government documents. You didn't file any petition with US government. Its the employer who petitioned showing willingness to hire you. Approvals are also sent to employer or Attorney (who then has to send it to employer). Then the employer needs to give you the bottom part of it (I-94) if you join them or if you have to apply for visa to enter the US. You didn't initiate any of these process, didn't sign any documents, so you cannot be held responsible.

What if you move to company B, company A has all your information from past, and using it company A files another I-130 without telling you. If this is approved, do you have  to move back? Absolutely not!

The conclusion:

You can continue to work for Company A and join company B on your convinience.

You can also say you don't want to work with company B any more and stick with company A, but in this case, if you need another 'change of employer' to company C you may first need transfer from company B to company A(I am not sure on this).