Well, at least they're trying to help! Definitely not as a wingman though. Haha sorry, OP.

or op all to themselves...

PLOT TWIST. Your teacher wanted to make you look bad so they could have the waiter all to themselves.

The teacher was right.

Even if all went great with the waiter, he'd tire of you speaking Spanish like Yoda.

Correct, the teacher was. OP's wingman, he was not.

Normally, a wingman plays up the pilot to make him more attractive to the target.

In the way of the Jedi, the X-wingman dumps on the pilot and creates pity in the target.

You could have said my Spanish teacher. If it wasn't for me looking at the comments, I wouldn't have understood this FML.

Wasn't it a bit awkward to begin with, trying to flirt with someone in front of your teacher?

To be fair , I am not a native speaker in English, but I suspect " my sentence's structure" is grammatically doubtful.

That usually isn't an interest block. Usually most people are happy that you want to learn and are looking for corrections if they are needed. You being foreign gives you an automatic sense of being exotic. Play it up a bit and be all like "sorry, I'm still leaning the finer arts of your (wonderful/lovely) language", and you might get a little bit further than you think. Best wishes!

That sounds really fxxxing cute to me.