I'm in a similar situation as you... I'm a newbie to manifestations.... but I'm currently using the technique to attract my ex who left me for another woman.  I think a crush very different (and much easier) to attract than an ex because with a crush, you really only have positive feelings about him.  A crush is usually only a fantasy... someone who has only brought you happiness.  Someone you love brings much more intense feelings.. the happiness is much stronger than a crush, but they can also bring you great pain.  I find it very difficult to push out all the thoughts of pain and anxiety.  Maybe you're letting those feelings pop in.  I know how incredibly difficult it is to block it out.  I constantly struggle with it too.  Just stick it out and remember how worth it he is!