The hard part is that you are embarrassing your Sensei and school...even more so than yourself. They were the ones that put you up to test after all, and the school that sent a poor quality Aikidoka up will be judged by the quality of student they present to the technical comity.
I've heard to many stories about Yamada Sensei, or other Technical comity members "having a word" with the Sensei of failing students. I've heard of Yamada Sensei "having a word" with students who had passed, but barely passed, black belt tests as well. So my only opinion would be is, if you are going to test, be prepared. I think you are gonna want to look like a black belt on the test coming off the bat. It is embarrassing to pass, but pass while struggling.
I have to completely "ditto" this. I have heard stories where Yamada Sensei failed everyone. My first winter camp with about 25 dan (shodan through sandan) tests Yamada Sensei only passed a couple of people on "merit" which he announced to everyone. The remaining testers after Yamada Sense spoke with all the sensei involved later on. The testers found out that they passed but only on "recommendation." And, they knew it, too. Yes, it's embarrasing, but if your sensei does not fully prepare you, but tells you that you are ready, then how do you know your not?