I recently brewed my first batch of beer. I knew I was not supposed to cover it completely however I did cover it slightly to keep my wort at a better boil. Steam was able to escape however I am worried it might not be enough and Dimethyl Sulfide may be in my batch. Is it safe to boil wort partially covered with a lid?

It is certainly safe to boil with a partially covered lid, but you may need to increase your boil duration. As long as it is sufficiently long you should be fine. Typically most of the DMS will be evaporated within 45minutes of a good open boil. I'd say if you boiled at least an hour and cooled your wort pretty quickly at worst you'd have a slight cooked corn aroma.