Heat Questions

tried a UTH but didnt work temp stayed in the 60s even with the UTH all the way across the bottom. and from what i understand from the reptile guy in hte shop, temp isnt such a thing atm for baby corns,but as it gets older and into a bigger tank it will need it . my snake is all of 13" max and in a small viv of 12x6x6 inches. inch of strata and lump of "looks like tree bark" to hide under with its water bowl. seems to eat ok had small pinkie sat then tue. will be feeding today.