Seized piston?

Hello everyone, This is my 1st post. wooohooo :aj: . Anyways I have an 88' RM250 I am new to 2 strokes. I rebuilt the top-end last wwek and it started up fine. Took it to a friends house to tune it in and of course I don't know what I am doing. So were making adjustment to the exh valve deal and topend screw and I am heavy on the gass. I keep it pinned open for about 3 seconds and when I let off the throttle the engine came to an abrupt hault. I try to kick it over but it seems the pistons seized up in the CYL. Just GREAT :|. I just got a LA sleeve instaleed and I put a new weiso piston in. I havent pulled the cyl yet. I was gonna post here to see what you guys think. Is it goona be bad? Do you think I could just replace the ring or is there more probably damaged. I am going to open it up soon. I just hate to think I blew $500 bucks. Thanks for any help guys.
Jason

I pulled the cyl off today and well its pretty bad. The piston rubbed the cly wall very hard. Both piston and cyl wall are scored. DANG IT! :( . I am going to take it back to the local shop to get it bored and honed. Also got to get a new Wisco poston :| . THanks for the insight Rm_Guy. All will be well when I learn about these deadgum 2 smokes. ;) Thanks