Hope is about possibility, wish is about improbability. Since it is unlikely a park can be made bigger, 'wish' is more appropriate than 'hope'
You can say (spoken) I wish it was somewhat/a little/a bit bigger. In writing you need to use the (shudder) subjunctive... I wish it were bigger. More easily 'If only it could be bigger...'
A simple question, a simple sentence, at first glance, but in fact not so simple!