Upvote:2
From your very experience, border officials can and do ask for proof of accommodation. Having included that with your visa application, it might be unwise to simply cancel. Telling a border official that you're now planning to stay with a friend might be a negative tick mark, as @GayotFow wisely points out.
You can:
- keep the reservation (whether you check in and shorten your stay to one night, or cancel after you enter and pay any cancellation fee);
- cancel and obtain an invitation letter from your friend (making sure it includes all contact information and, perhaps, the reason for the last minute invite, as opposed to when you were planning your trip and visa application);
- cancel the reservation in advance (and take your chances that you won't be asked about it when you present for entry at the border, and if you are, it won't be an issue and, if it is, not one that results in the IO refusing entry).