Hi there. I went to Disneyland in March-2 months and about 10 lbs ago. I weighed about 260 when I was there. I am just a tad taller than you. I know everyones measurements are different, even two girls weighing the exact same thing/same height but....
I fit in the rides at 260 and 5ft7. Granted it was snug but there wasn't ever any ride operator that even looked concerned that wouldn't fit. My a** fit in all the seats and the seat belt fit around me/ride bar could click close without any crazy sucking in of my gut.
I personally think you will be fine!!
Also, wear comfy shoes and bring a backpack for bottles of water, sunscreen and healthy snacks. They charge an arm and a leg for those items bought in the park. I got blisters the first night as I forgot to pack my tenny shoes, didn't want to miss anything the first night we got there. We didn't go buy new shoes for me until the next day when we could find a Target close by.
Another good tip: If your room is close by, plan for an afternoon seista for you and any little ones. A two or three hour break makes all the difference. The park is open quite late and for me it would have been impossible to stay for the fireworks had I gone non-stop all day.