I can't say whether 2 mL of BB/BA (in a 20/5 ratio) plus 3 mL of oil can dissolve 2 grams of trenbolone acetate, because I haven't tried that combination and it's not possible to extrapolate accurately.
But 2 mL of BB/BA in that ratio, plus 8 mL of oil (a total of 10 mL) definitely cannot hold 2 grams of trenbolone acetate. It will hold about 1 gram.
If the earlier, less-oil mixture actually did hold the 2 grams of TA, it would precipitate (crash) out in not that much time after adding the further 5 mL of oil.
If that's not happening, then the first 5 mL (2 mL of BB/BA, 3 mL of vegetable oil) only dissolved the first 1.0 grams, approximately, of TA.
In other words, you could use more BB, BA, and vegetable oil, and get about twice as much final product at the same actual concentration for the same amount of Finaplix.
So far as your basic method, other than the numbers, the general idea is fine. It's a reasonable expectation that, for example, 2 mL of BB/BA plus 3 mL of vegetable oil, or 4 mL of BB/BA plus 6 mL of vegetable oil, will probably hold at least as much TA as would be the case with mixing all the oil in in the first place.