sexing scans

I'm 16 weeks and 1 day today this is mine and my partners first baby and on Monday I have been booked in for a sexing scan by my partners mother which then I will me 16 weeks and 3 days what do people think on sexing scans as I'm a little concerned as I don't want to find out if its a boy or girl go and go buy pink or blue things and then I find out it's wrong and I have brought all the wrong things I will be asking to confirm on my 20 weeks scan anyway what are everyone's thoughts on these scans? Xx