This isn't Peru or Argentina or Nicaragua. In places a newbie is likely to go having someone close by, bi-lingual is crucial for "negotio" business (ventas) sales, and el saldo de banco (bank balance). I spoke "Ingles" yesterday for the first time in four or five months (I stumbled on verbs).
Be patient and smile. Here in Mexico the idea of a turista sans la idioma is actually expected. I've run into situations where the tourist speaks Spanish and the Mexican responds in English. It is hilarious. Both are practicing.
But the ability to not speak Spanish should not enter your vaguest doubts. I was so uneducated about the languages 50 years ago I had no idea that the word "No" was identical in both languages. I had to ask!
Mexicans are gracious unlike the French with the butchering of their tongue. Even a botched attempt a fledgling flapping of Spanish will be received with a pleased smile. Mexicans see it as a definite sign of respect and that will bridge almost any obstacle.
"Ay me yoy para mi cuñado" doesn't sound like much but it means a person is going to round up his brother-in-law who just returned from the states.
Technical doctor spanish is not easy even for me. I cannot even figure out what my USA doctor wants to say half the time. Don't feel bad. Young ladies are absolutely the worst for attempting to understand "foreign looking folk speaking Spanish"
A young lady kept replying ¿Mande? ¿Mande? (What? What?) to my questions about whether they carried gringo ketchup. Mexicans standing in line rolled their eyes. Finally I said "¿Te hable Español?" (Do you speak Spanish?) to get her attention. She turned beet red, then instantly answered the question. The Mexicans in line, were howling in glee. So don't let it get to you if a young girl acts like you just fell off a flying saucer. Someone will help you, trust me.
When I go places where only Indian idioma is spoken (lots of off the beaten track places) I have to search for an indigena who speaks for instance Tzotzil and Spanish. I do not let it stop me a bit.
Part of the reward you are going to get are the fond memories of folks who will stand on their head to be able to communicate with you!