To prepare 100 g of 6% by weight solution you should take 94 g of trifluoroacetic acid and 6 g of dry chitosan.

You do not need any molecular weight if you want to prepare % w/w mixtures. If you anyway want to know about molecular weight of chitosan, use the molecular weight of the chitosan repeating unit considering the deacetyation ratio..

It would be advisable to clearly discriminate between what, in principle, could be either; ― (i) a concentration (mass) ratio for a solution or colloidal dispersion, where the reference mass is that of the solution or colloidal dispersion; (ii) or a formulation (mass) ratio, where the reference mass is that of the solvent or fluid, thus taken without the solute or dispersed solid.

Thank you immensely for the ideas. Prof Migorod, I thought i was making wrong calculations of the concentration hence the reason for the clarification.