One can pick using any number of right hand patterns. For really fast tremolo it is usually better to alternate because it makes no sense to think that one can use the same finger twice at a high speed. Of course there are exceptions to every rule. I would request that you post a picture of the sheet music so we can see what you are doing. It is diffcult to form a clear idea based on the wording (at least for me).
There is a reason for the fingerings and for practicing them the way they are written. The classical guitarist needs to be able to control the speed, tone, phrasing, and dynamics of a tremolo, or any other technique. Some patterns may feel unnatural to first but all it takes is practice to get them up to speed and even.
Things to watch out for include,
galloping (uneven rhythm in an alternating pattern)
inconsistent volume (some notes being slightly louder/softer than others)
unwanted accents (a note here or there being accented even though it's not supposed to be)
buzzing or scraping (this is usually due to poor placement of the finger right before plucking)
In my opinion you are developing a bad habit. There are many guitarists that take the attitude that whatever finger is available is fine to use as long as it feels okay. This does not lead to mastering the instrument and the techniques of the instrument. In the long run avoiding the written fingering and defaulting to whatever happens means you will not develop the kind of clean technique and control you need for harder pieces.
If you are serious about mastering classical guitar you should work on all right hand patterns, i-m-i-m-..., m-i-m-i-..., i-a-i-a, ..., i-m-a-m-..., p-a-m-i-..., etc.
I personally have never seen a steady stream of notes with a repeated finger. But you stated that this is "after each bass note". We need to see the entire sheet music to really understand what you are doing. Are the bass notes plated with the thumb? I would guess so, but I've seen examples where the other fingers are used.