So you are using the Integer to ASCII (AIC) instruction for 12 and 3?
You could use the Concatenate (spelling?) ACN instruction and just combine 12, "." and 3 together to get 12.3
Do your math to get the whole number, and the decimal as an integer, which you appear to have already. Then just take the three strings (third being the "." point) and combine them all into a single string in the correct order.