all such things can be solved by css. You need to study the source of the page to figure out how to change the css to do what you want.

typically a feature will have a custom class on a container div somewhere, so for survey probably something like 

.survey textarea { width: 350px; }

or if not a textarea then

.survey input[type="text"] { width:350px; }

If you don't like some things about the Survey feature you may want to consider purchasing Form Wizard Pro which is also suitable for surveys and has a lot more flexibility. I have no future plans to ever improve the free survey feature we include in mojoPortal because I make my living selling the add on features. You can try Form Wizard Pro on our demo site to see how it works.