Linear regression: Stopping a continuous independent var being treated as ordinal

#1
I have a simple multiple linear regression equation where the independent var "ux" has every value listed separately in the summary:
mod1<-lm(b.xen~ux+kg+sex+age+d_categ+consciousness+airway+cm+goj)
summary(mod1)

"ux" is in centimeters. The problem may arise from the measurement only being accurate to the nearest cm rather than XX.y. I am assuming R has presumed that each "ux" value is therefore a nominal category, whereas it's really a continuous variable that simply can't be measured to a high degree of accuracy.

How do I force R to treat "ux" as continuous?
Thanks,
Stephen