do i evolve my lvl 75 squirtle?

probably a dumb question but im still new to all this. i like squirtle bc hes cute so i decided to do a squirtle only run and not to evolve him. ive made it this far but it feels like i struggle a little since my hp and sp atk are not too great, plus i got earthquake but only blastoise can learn it. have i already missed out on the stat increases i would have earned if i just regularly evolved? is it worth evolving now before the e4?