It could be. Once again the problem is the lack of context.
Ganhar - to win or to earn
Vou ganhar um relógio como prêmio da competição. - I will get (win) a watch as a prize from the competition.
Vou ganhar um relógio se eu fazer minhas tarefas. - I will get (earn) a watch if I do my chores
Ganhar - to receive, used specifically with gifts.
Eu vou ganhar um relógio no meu aniversário. - I will get (receive) a watch on my birthday
Mm...theoretically, I guess so, but the chances are you'll be misinterpreted, I think. What do you really mean by saying it? If you mean you'll go buy a watch, I would have said "vou comprar", and if you mean you'll find a watch in your closet, maybe "vou achar".
Even for the English "I'll get you a taxi", I think I wouldn't have used 'ganhar' although it might work out. I'd probably say "vou procurar" or "vou achar" in this case.
(I'm not native -- others might correct me!)
Why not "obter" or "receber" (to get), both of which are offered on a translation app? Surely these would be closer to the actual translation than "ganhar" (to win)...!