Accidentally took 20mg of flexeril (cyclobenzaprine hcl) and hydrocodone/ibuprofen 7.5-200mg for my chronic back pain. is that too much?

Yes: Try very hard to avoid such accidents. They can be serious. 20mg is a high single dose. Neither is intended for more than short term. The combo increases chance/severity of side effects. Definitely talk to Dr who gave the Rx(s) for clear safe instructions. I hope your pain finds relief, but it may need things other than drugs. Be careful, best wishes!