My COPD is flaring up, can I go ahead and take my left over prednisone?

Yes and No. Prednisone is a good drug for COPD exacerbations but you should not start it unless you check with our healthcare provider first. COPD exacerbations may also require antibiotic therapy and an increase in your inhaler frequency. It is always best to check in with your doctor before starting on prednisone.
NOT A WISE IDEA. Prednisone as you are aware is a very amazing medication but it has many side effects. If you are sick enough to be contemplating prednisone, you should see your doctor and let them evaluate you and decide how to proceed. Good luck.
Ask your doctor! Please consult with your doctor before doing this; because the medication may be expired. Always a good idea to check in with your doctor any time a chronic condition(eg copd, colitis, etc.) flares up.
Need evaluation ... You need to see your doctor because COPD exacerbations can have different causes requiring different treatments. And, steroid therapy may not be the right treatment for your current exacerbation. For example, some COPD exacerbations are due to infection requiring antibiotic therapy. This is why you need to see your doctor for evaluation and the correct treatment.