What can you do about it now? It is what it is. You're not applying to surgery or OB so it will somewhere between a slight bummer to totally irrelevant.
2nd- how bad is a comment- " student needs to read more"
The last refuge of the surgery attending scoundrel.
PDs interpret this as "I barely remember this student...pretty sure s/he didn't kill anybody and only broke sterile field a few times the first week...I have to say something useful here...I know, needs to read more".
Everyone needs to read more including the attendings. The comment might also come in a different flavor as "needs to increase fundamental knowledge", so don't be too alarmed if you ever come across.
I don't read the MSPE when interviewing applicants. I care about two things: letters of recommendation and personality.
I am not sure if the PD looks at the MSPE when deciding who to interview, but I doubt it.
All this, of course, will be speciality and program specific. But I wouldn't swear it. Focus on the things you can change and that have more weight (board scores, letters, etc).