Dear {Recipient},
I'm sorry for the inconvenience I may have caused you last {day of the week}. I didn't want to bother you, but there was no way I could {do action} by myself, so I had no choice but to ask for your help.
Thank you for obliging me despite your own busy schedule. Your assistance really meant a lot to me. I have {enclosed/included/attached} a {gift certificate/movie ticket/etc.} as a token of my gratitude.
Warmly,
{Your Name}