last summer on tandem we took on a very challenging hill on a 80-90 mile ride.
At one point we stood up to go up a hill (not the big one) but we were in the wrong gear. so my weight went the wrong way and i wrenched a knee.
By the time we'd gone over the worst part of the hills, my knee was really hurting and scaring me. SO at the next rest stop, with 12 flatter, windy, hot miles to go, we decided that i'd had enough.

Nope, no regrets. And for the next month, i was careful and my knee healed.

You did the sensible thing!