I have a small mouth so when I smile it looks disproportionate with the rest of my face what Can I do to have a bigger smile?

You are an excellent candidate for a DNA Appliance and Epigenetic Orthopedics to 3 dimensionally grow both your maxilla and your airway to create a full wide health smile.  This will also grow your nasopharyngeal airway by a process called Pneumopedics.Neuromuscular dentistry and ceramic restorations can also do an excellent job of creating a full wide smile but won't truly address the airway.I suggest finding a neuromuscular dentist who utilizes Epigenetic Orthopedics /Orthodontics.It is ot uncommon to see eyelids higher and appearance of bigger eyes as an effect of the process.  The deep naso-labial lines and dark circles will usually correct as will most forward head position.

I would suggest porcelain veneers to build out your smile. Proper contouring by a good cosmetic dentist with a good lab should broaden your smile quite nicely. 

Hi:From the pictures, it appears that you have small upper arch.  You might want to consider 10 upper veneers to increase the width of the arch and imporve the color at the same time.  It’s best to consult with an experienced cosmetic dentist specializing in Anti-Aging Dentistry.Best,Dr. Maddahi

Healthy looks good. 
If your smile looks ‘small’ , then there is likely value in seeing a physiologic Dentist to see what’s going on.  
Short answers is, with Orthodintics, or Crowns/Veneers or a combination of both... you could have an ideal smile that is both healthy, functional and could be full and wide like you’re hoping for 

Based on your photo, it appears your teeth are in good alignment, otherwise braces or Invisalign can widen your smile by pushing the back teeth out.  In order to produce a "bigger smile", there are a couple of ways you can achieve this.  You want to address what we call the "buccal corridor" or "negative space".  This is the dark space you see between your teeth and your lips/cheek towards the back when you smile.  An esthetically pleasing smile displays teeth that almost rest on the lips, like Julia Roberts.  To eliminate this space, porcelain veneers or composite bonding can be added onto the outer surfaces of the teeth.  You may also want to consider slightly "lengthening" the edges of your upper front teeth.  Generally the edges of the upper teeth approximate the upper border of the lower lip. But at the same time you want to be careful because teeth have an average length of 10-11 mm, so you don't want to make them TOO long.  It's helpful to have 3 other photos as references - a frontal photo in which your lips are slightly open and relaxed (lips at rest) to see how much upper front tooth edge is displayed (rule of thumb is 2-4 mm), one where you can see the entire tooth and gum line to see how long the teeth are, and a lateral/profile view of your smile.  

Based on the photos, you appear to be a good candidate for porcelain veneers to improve the shape and color of your teeth. Also, veneers can widen your smile. Seek an experienced cosmetic dentist who has great photos and reviews.

Hi,
You can highlight your smile through the veneers in 10 teeth above and 10 below. Your choices, with our advice, the size, color and shape suitable for your teeth and your face.you will achieve your desired smile

Occasionally what seems to be a small smile can be made wider and fuller eith porcelain veneers
Because you currently show 5 possibly 6 teeth and ideally you should show 8 to 10 teeth for that fuller wider smile. 
In your case I would recommend widening the arch and lengthening the teeth... with porcelain veneers  you can have that fuller smile!