Add an extra 16th note in a measure?

I wanted to make an orchestral version of a song someone already wrote, to see what it would sound like. But I've run into a problem. On one part, there is a half note, then a quarter note, then an 8th note, then 3 16th notes in one measure. When I try to put it in musescore, I can only fit in two of the 16th notes. Is there something I can do or is this the end of the road?

http://judaspriest.com/tabs/images/rockhardridefree6.jpg

That is the link to the sheet music. I'm stuck at the measure that starts with A minor.