Creatinine 0.77 (ref: .70-1.2) bun/creatinine ratio 14.3 (ref: 12-20), gfr greater than 90, but creatinine in 24 hr urine elevated 2.1 (ref: 0.8-1.8). is this indication of a problem with my kidneys?

No, you are not drinking enough water. All laboratory results need to be interpreted in the clinical context and the doctor who ordered the tests is usually in the best position to do that. Talk to the doctor who ordered the tests. Having said that, drink enough water daily so that your urine is mostly colorless. Wish you good health!

The low or high creatinine in 24-hour urine collection is due to error in collection, not exact a 24-hour urine output. High creatinine in the urine isn't a reason to concern, either your urine collected volume was more than 24-hour period or you have a high creatine intake which is more common in male body builder. The 24-hour creatinine clearance will be much higher than the eGFR by formula.

@.1- when normal is up to 1.8 can be a slight variation =in view of all other tests being excellent. You seem to have OK kidneys. You can repeat the 24 hr. creat. in 6 months if worried