hi there
I was annual passholder for Disneyland so I go just about every weekend (It's past time to renew). I was 5'4 and 310 pounds and there wasn't a single ride there that I couldn't comfortably fit on. Disneyland is really plus size friendly.
Go... and definately enjoy yourself
You'll walk so much you'll have dropped 5 pounds by the time you get home (and you'll have enjoyed every moment of it)
Keep in mind that pretty much all of the food there falls into the "not a wise choice" category so you might want to consider stopping in at the nearby grocery store to get some "carry in" snacks... and there is an IHOP, Denny's, and a few other restaurants just outside the park. If you don't mind the walk, you'll save yourself a ton of money and you'll have alot more options.
If you want to ride space mountain, make sure you get that speedpass earlier in the day. There's usually a 4-6 hour return time...so you can be out riding other rides instead of waiting in line for 2 hours.
One thing almost nobody knows.... If you buy something inside the park and don't feel like carrying it around all day, you can ask the cashier at the gift shop to ship it to the news stand at the front of the park. You can pick up your purchases on your way out at the end of the day.