Good points by Hisbiscus.
Wash hands well with soap that has no fragrance, lotions, or dyes. These chemicals will interfere with wafer adhesion. I use Cetaphil bar soap.
With clean hands, now carefully scrub the peristomal skin around your stoma using the same soap. Be extra careful around stitches. Rinse and pat dry with paper towels. Now use adhesive remover wipe to carefully remove any residual adhesive remaining around the stoma.. careful around those stitches. Use a finger, and highly press the skin down around your stoma. As you pull your finger up, If it feels sticky anywhere, use another remover wipe. Check again.
I use a Hollister 2 piece like you. But I have a colostomy, so much less of a leak problem. Illeostomy is harder to leak proof.
You might try a moldable barrier ring instead of paste. I use Coloplast Brava moldable ring, 2 inch diameter. You might have to wait until your stitches are removed. You don't want to pull anything out.
Advantage of the ring is you can cut a larger wafer hole. The ring seals against the stoma, wafer seals to the ring. You can also add a ring to the top of the wafer, sealing the stoma. This way you have a double seal. A ring under the wafer, and one on top.
Are you using a support belt? Hollister makes a thin elastic belt that clips onto the bag, holding it secure. I wear one everyday.
There are also wider support belts. Nu-Hope corporation makes a variety of belts. Many Ostemates put on a belt for an hour or so after a wafer change.
Also hold the wafer against your stomach on the side opposite your stoma for a minute to warm it up, then remove the plastic backing and fit it onto your stoma.
You can order support belts from your ostomy product supplier.