Help! Need an Excuse!!!?

Ok, my guy friend Dakota Ive known since 6th grade, were in 8th now, likes me, he asked me out and I don't like him like that! I don't know what to do! I told him I was grounded from dating as my original excuse but he asked my best friend and without thinking she said "Lexi's not grounded from dating!" and hes still asking me out, he asked me to hang at the park this weekend cause Im busy on the weekdays, and I need an excuse not to hang out with him! HELP!