Eeeeeh yes. If you want to quote the "rules" then you need to pick a playable race. By playing a magic dinosaur you've already stepped outside of the rules.
This is simply factually incorrect. The Other Races page I linked in my first comment does have rules for playing a monster with hit dice, and the awaken spell is a buff spell with instantaneous duration, which, albeit subject to availability and cost by the necessity of having it cast by someone else than the player character, is still most definitely within the rules, and it was these specific rules, which both exist and which I linked to, which I wanted clarification on.
Playing as a non-humanoid starting the campaign with an instantaneous buff spell applied to them is unusual, yes but the race, the spell, and playing a monster pc all have rules. It being unusual doesn't make these rules stop exist.
CR is s guideline and doesn't apply to player characters. Ask your GM if you can have more Hit Dice than your party members.
Not only can a monster as pc have more Hit Dice, the rules for that circumstance suggest increasing the disparity in Hit Dice further by giving extra class levels every 3 levels.
Nothing said in the forums amounts to anything if the GM says no.
This is true of this case. It is also true in every case. In my initial post, I did not ask for advice on what you believe my gm would or would not say no to - I asked about existing rules which I were unsure about.