My b-12 shots expired 3 months ago but i kept it in the fridge sense i got them, i just got one shot is their any danger?

The Danger is it is very unlikely you need B12 at all at your age. But if it is clear you do get fresh bottle. Assuming you hand not inserted a needle in after you have drawn it out or used it likely no problem. If it is cloudy discard.

It depends on why are you getting the shots. To avoid getting B12 deficiency while waiting to get the shot you may wish to sub-lingual form of B12. It is available over the counter and can bypass the absorption issues in the intestine. For info: https://pubmed.ncbi.nlm.nih.gov/30632091/