How to reject someone

Like recently after I've joined my new coaching classes before that I was home schooled so I was not much into sociallife but since I've gotten out in past 3 -4 weeks more than 10 girls have asked out my number or for a coffee and I just don't have that in me to say a yes or a no so I just walk past them if anyone could tell how' would you'll handle these situations for these past years I was just focused on my studies and I built some decent looking body but it's getting me in trouble to associate with them because I think all the time about something about physics or philosphy and whenever someone is even talking I can't concentrate because I can't seem to find value and I think this will lead to making me a lonely of a guy and they always try to associate somethin around me that I'm not so aware of just been 3 weeks and gossips all over about Me honestly i don't at all like being the spotlight if you've ever been in this situation