Is this happening on all rolls? I can see getting a Forward or Backward roll confused with playing triplets but this shouldn’t happen on an Alternating Thumb roll.
How long have you been working on them and how many different rolls? I suggest getting one thing down correctly before starting another, or start another when you absolutely can’t stand to work on the first any more.
Rolls like any other technique take some time and many,many, many repetitions to get use to. It can take many thousand repetitions for some rolls to be in time (this is usually the case with anything for me) .
Do you have a metronome you could use? This does the counting for you…I suggest setting it at one click per note, that way there is no counting unless you have a quarter note n the roll (this would be two clicks).
You may be trying to play too fast.
Hope this helps some. Have patience, it takes a while, but getting it down right from the beginning really pays off in the long run. I might could help through Skype if you have it also.