125 cc engine, 64" propeller 3 blade, 180 kg gross weight, will it climb?
I found a google site that showed: Honda GC 125 - 124cc, 10.8 bhp, @ 9000 RPM. 

Seems to me it would be much less at 3000 RPM. Can you use pulley/belt system to achieve high engine RPM (smaller pulley) and lower prop RPM (larger pulley)?

The frontal area you provide:

wings length is 29' feet and width is 4'6" (54") approximately, 

sounds similar to a Cessna 150, which has a narrower cabin (just about two adult shoulder width, 38 inches), and that needed 100 HP to fly, coming from a 200 cubic inch engine.  It's overall weight was higher tho, 1600 lbs gross (in my 1971 model) vs the 250kG/552lb you provided. If the extra 16" of width is all in the cabin, that will be a lot of extra drag to overcome with that low horsepower engine.