You can enter the Given Name as listed in the passport and not worry about the last alphabet being not included due to DS-160 character limitation. This is absolutely fine as the CO will look at the passport for identification purpose.
If there is no surname in the passport, you will leave it blank in the DS-160. It doesn’t say to enter your given name in the surname if no surname, right?
For example wife may have two surnames after marriage (Fernandez Garcia) , and the instruction in the DS-160 says to enter all surnames listed in the passport but if it is only one surname, list that.