Most likely the limit screw or cable.
If you're knowledgeable about bike mechanics, give it a go. If not, take it back to the shop. They should fix it at no charge.
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The Lord is merciful and gracious, slow to anger and abounding in steadfast love. - Psalm 103:8
I am a cyclist. I am not the fastest or the fittest. But I will get to where I'm going with a smile on my face.