It is difficult to say what the note was. You would have to determine how many steps above F the note was. If your slide was still in 1st, it may have been the next note up in that position.

There are several notes higher than the high F. If you were in first position, you most likely played a high B flat, which is still impressive. You should know, however, that though it is awesome to have an extended range, you should focus more on practicing tone quality and intonation. Also, it's one thing to play a high note, it's another to have complete control over a high note. I'm still working on it (the high B flat) and I'm a Senior in high school (though I didn't learn how to play the trombone until two years ago). The range on a trombone is incredible. The high B flat is no where near a trombone's limit. If the trombone has a limit, I don't know what it is. I do know it can go up to a super G (which would be like 10 lines above the staff...)...which is 5 lines above the high B flat. I have no idea what position this is. I only know how to play up to a high B, which is 2nd position. Through experimentation, I have been able to play one overtone above the high B flat, but I don't know what it is, and I have very little control over it, thus I don't consider it part of my playing range.

Some background info: When any instrument plays a note, a set of overtones (notes higher than the note by a specific ratio) also ring out. The varying strengths of these overtones give instruments their unique timbre. As a trombonist, your first position notes are the notes of that overtone series (individual notes in the series are called partials). When playing the fundamental, the note the overtones are based on, it is known as a pedal tone. For the trombone, the fundamental is 2 octaves below tuning Bb. In general, the human ear hears less overtones as you go higher. This is one reason why tone quality tends to suffer as you play extremely high. The note you played was probably Bb. However, it may have been an Ab, in which case in would have been extremely flat. It is rare in most cases for a trombonist to be required to play above High F. However, in some orchestral works (Ravel's Bolero for instance) you may be asked to play up to a high D, and jazz works can go a bit farther than that. A good list of partials in all positions can be found at http://www.ulm.edu/~everett/studio/charts/bbovertone.pdf. The higher notes are notated in tenor clef. High F is in the spot tuning Bb rests on in bass.