Quite seriously, I have to recruit people in my job (which isn't aviation - yet!) and the CV is the first impression that I get of that candidate.
My view is that spelling and grammar DO matter and if you have any doubt, get someone else to run their eye over your CV for any errors. You might not have a second chance.
Spelling and grammar is one issue that seems to polarize the Pprune community. However, we should accept that we all type things in a hurry and, whilst I try to be careful, the odd typo can always slip through! However, your CV should not be done in a hurry so, have an an@lly-retentive pedant such as myself, check it. If you recognise that spelling ain't your strong point, then don't feel ashamed in asking for help.
Cheers
Whirlygig