How can I correct this?

MuseScore deliberately put those slashes there because it represents "tremolo", which is usually the only way non-sustaining instruments like guitar or mallet instruments can sustain notes. To get rid of that, if you change the note from a half note to a quarter note, then it would get rid of the tremolo, since the guitar player would no longer have to sustain the note.

Alternatively you could use a different type of tablature. The tab you're using is "full", but there is also "simple" or "common".

Indeed, this display leads to confusion (there is some other threads on this subject)
This arises by using the Tab 6-st type "Full". By default, the stems of half notes are shown like this (and indeed, at first glance, this may seen as a tremolo). This is not a tremolo at all, it's by design (it worths to continue to be discussed, if exists another better solution)

To change this: right-click on the Tab staff -> Staff properties -> Advanced style properties -> Note Values -> Half notes:
Either: tick "None". But not the aim probably? Depends the context (how many different notes values eg) in your score
Or: always in Note Values -> Stem style -> tick Beside Staff -> Half notes -> tick "As short stem" -> OK
But in this case, you return with the type Tab 6-st type "Common".
A choice to do.